Establishing continuity between a shield within an implantable medical lead and a shield within an implantable lead extension

ABSTRACT

Implantable medical leads and implantable lead extensions include a shield. The implantable medical lead is coupled to the implantable lead extension. Stimulation electrodes of the implantable medical lead contact stimulation connectors within a housing of the implantable extension to establish a conductive pathway for stimulation signals from filars of the implantable extension to filars of the implantable medical lead. Continuity is established between the shield of the implantable medical lead and the implantable extension by providing a radio frequency conductive pathway within the housing. The radio frequency conductive pathway extends from a shield of the implantable extension to a shield connector that contacts a shield electrode of the implantable medical lead. The radio frequency conductive pathway may have various forms such as a jumper wire or an extension of the shield within the implantable extension.

RELATED CASES

The present application claims priority to and incorporates by referencethe following, each as if rewritten herein in its entirety: U.S.Provisional Application 61/174,204 filed on Apr. 30, 2009; U.S.Provisional Application 61/174,216 filed on Apr. 30, 2009; U.S.Provisional Application 61/174,224 filed on Apr. 30, 2009; U.S.Provisional Application 61/174,234 filed on Apr. 30, 2009; U.S.Provisional Application 61/174,247 filed on Apr. 30, 2009; U.S.Provisional Application 61/174,254 filed on Apr. 30, 2009; U.S.Provisional Application 61/174,262 filed on Apr. 30, 2009; U.S.Provisional Application 61/174,276 filed on Apr. 30, 2009; U.S.Provisional Application 61/174,287 filed on Apr. 30, 2009; and U.S.Provisional Application 61/174,296 filed on Apr. 30, 2009.

TECHNICAL FIELD

Embodiments relate to implantable medical leads and implantable leadextensions that include shields. More particularly, embodiments relateto establishing continuity between the shields of the implantablemedical lead and the implantable lead extension.

BACKGROUND

Implantable medical systems including implantable medical devices (IMD)and associated implantable medical leads provide functions such asstimulation of muscle or neurological tissue and/or sensing ofphysiological occurrences within the body of a patient. Typically, theIMD is installed in a subcutaneous location that is accommodating andrelatively accessible for implantation. For instance, to providestimulation near the spine or pelvis, the IMD may be installed in apocket located on the abdomen or upper buttocks region of the patient.The implantable medical lead is installed, either through a percutaneousprocedure or a surgical procedure, depending upon the type of lead thatis necessary.

Once installed, the lead extends from the stimulation site to thelocation of the IMD. The separation of the stimulation site to thelocation of the IMD varies, but may typically range from about 20 cm toabout 100 cm. For relatively lengthy separation, if a lead of adequatelength is unavailable then a lead extension may be implanted to spanfrom the IMD to a proximal end of the implantable lead.

The implantable medical lead includes connector rings on a proximal endand electrodes on a distal end, and conductive filars interconnectingthe electrodes at the proximal end connector rings to the electrodes ata distal end. The lead includes a jacket, often made of a flexible butbiocompatible polymer, and the filars are insulated from the body tissueby the jacket. However, the filars are not insulated by the jacket fromthe presence of electromagnetic radiation. Electromagnetic radiation inthe radio frequency (RF) spectrum induces currents into the filars andthus presents current at the electrode that is unintended. In thepatient's normal daily experience, the level of RF radiation that isencountered is at a negligible level, and there is no danger of heatingof tissue by the unintended current that may result.

RF radiation poses a risk to tissue in contact with the electrodes whenthe intensity is significantly higher than the background levels. Thesurface area of each electrode is relatively small so that a smallamount of tissue must dissipate a potentially large amount of inducedcurrent. In particular, if the patient is exposed to the RF radiationfrom a magnetic resonance imaging (MRI) scan, there is a highprobability that tissue damage at the stimulation site(s) can occur.This tissue damage may be very dangerous, particularly so forneurological tissue. Therefore, patients with IMDs are typically notpermitted to have a body coil MRI scan for at least these reasons.

SUMMARY

Embodiments address issues such as these and others by providing animplantable lead and an implantable extension that include a shieldwithin the jacket that may reduce the amount of current induced on thefilars within the lead and the extension. The shield of the lead and theshield of the extension may be interconnected in various ways tomaintain the continuity of the shielding being provided.

Embodiments provide a method of shielding an apparatus comprising animplantable lead coupled to an implantable lead extension. The methodinvolves providing a non-conductive housing at a distal end of theimplantable lead extension that includes an opening, a connector withinthe opening, and an RF pathway from the connector to a shield within theimplantable lead extension. The method further involves providing ashield electrode on a proximal end of the implantable lead that has anRF pathway to a shield within the implantable lead, and inserting theproximal end of the implantable lead into the opening to establishcontact between the connector of the implantable lead extension and theshield electrode of the implantable lead.

Embodiments provide an implantable medical apparatus that includes animplantable lead extension comprising a non-conductive housing at adistal end of the implantable lead extension that includes an opening, aconnector within the opening, and an RF pathway from the connector to ashield within the implantable lead extension. The implantable medicalapparatus further includes an implantable lead comprising a shieldelectrode on a proximal end of the implantable lead that has an RFpathway to a shield within the implantable lead, the implantable leadbeing positioned within the opening so that the connector of theimplantable lead extension contacts the shield electrode of theimplantable lead.

Embodiments provide an implantable lead extension that includes anextension jacket and a shield within the extension jacket. Theimplantable lead extension further includes a non-conductive housing ata distal end of the extension jacket that includes an opening, aconnector within the opening, and an RF pathway from the connector tothe shield.

DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an embodiment of an implantable medical system thatincludes an implantable medical device (IMD) coupled to a leadcontaining a shield.

FIG. 2A shows an embodiment of an implantable lead with the shieldrevealed.

FIG. 2B shows the embodiment of the implantable lead in cross-section toreveal the shield and filars.

FIG. 2C shows an embodiment of the implantable lead with the shieldrevealed and with various parameters being specified.

FIG. 2D shows an embodiment of the implantable lead with dual braid wirewindings.

FIG. 2E shows an embodiment of the implantable lead with braid wireshaving a round cross-section.

FIG. 2F shows an embodiment of the implantable lead with braid wireshaving a rectangular cross-section.

FIG. 2G shows an embodiment of the implantable lead with braid wireshaving an oval cross-section.

FIG. 2H shows an embodiment of the implantable lead with the leadterminating at a given spacing from a nearest connector and a nearestelectrode at the proximal and distal ends.

FIG. 3 shows an embodiment of an implantable medical system thatincludes an implantable medical device (IMD) coupled to a leadcontaining a shield.

FIG. 4A shows an embodiment of an implantable lead with the shieldrevealed.

FIG. 4B shows the embodiment of the implantable lead in cross-section toreveal the shield and filars.

FIG. 4C shows an example of the implantable lead with a portion of theshield exposed near a proximal end of the implantable lead.

FIG. 4D shows an example of the implantable lead with an externalelectrode providing a coupling to the shield.

FIG. 5A shows a side view of an embodiment of an implantable medicalsystem where the shield of the lead is grounded to a can of the IMD.

FIG. 5B shows an end view of the embodiment where the lead passesthrough a connection block having a set screw to ground the shield tothe can.

FIG. 5C shows an end view of the embodiment where the lead passesthrough a connection block having a spring loaded connector to groundthe shield to the can.

FIG. 6 shows an example of a spring loaded connector.

FIGS. 7A-7C show side views of embodiments of an implantable medicalsystem where the shield is grounded with an external wire to the canover a direct current pathway.

FIGS. 8A-8C show side views of embodiments of an implantable medicalsystem where the shield is grounded with an external wire to the canover a capacitively coupled pathway.

FIGS. 9A-9F show side views of embodiments of an implantable medicalsystem where the shield is grounded within a header of the IMD to thecan.

FIGS. 10A-10C show side views of embodiments of an implantable medicalsystem where the shield is grounded to a ground plate on the header ofthe IMD.

FIG. 11 shows an embodiment of an implantable medical system thatincludes an implantable medical device (IMD) coupled to a leadcontaining a shield.

FIG. 12A shows an embodiment of an implantable lead with the shieldrevealed.

FIG. 12B shows the embodiment of the implantable lead in cross-sectionto reveal the shield and filars.

FIG. 12C shows an example of the implantable lead with a portion of theshield exposed at a point distant from the distal end of the lead.

FIG. 12D shows an example of the implantable lead with an externalelectrode providing a coupling to the shield at a point distant from thedistal end of the lead.

FIG. 12E shows an example of the implantable lead with a portion of theshield nearly exposed at a point distant from the distal end of thelead.

FIG. 12F shows an example of the implantable lead with a portion of theshield exposed or nearly exposed at a plurality of points distant fromthe distal end of the lead.

FIG. 12G shows an example of the implantable lead with a plurality ofexternal electrodes providing a coupling to the shield at a plurality ofpoints distant from the distal end of the lead.

FIG. 12H shows the embodiment of the implantable lead in cross-sectionto reveal the shield and the external metal conductor in contact withthe shield.

FIG. 12I shows the embodiment of the implantable lead in cross-sectionto reveal the exposed shield.

FIG. 12J shows the embodiment of the implantable lead in cross-sectionto reveal the shield and the metal conductor nearly contacting theshield.

FIG. 12K shows the embodiment of the implantable lead in cross-sectionto reveal the nearly exposed shield.

FIGS. 13A-13C show metal conductors of various types for attachment to alead to provide a coupling to the shield.

FIGS. 13D-13F show metal conductors having various configurations ofnon-conductive coatings for attachment to a lead to provide a couplingto the shield.

FIG. 14A shows the embodiment of the implantable lead in cross-sectionto reveal the shield and an outer doped jacket layer.

FIG. 14B shows the embodiment of the implantable lead with a pluralityof points with the outer doped jacket layer.

FIG. 14C shows an embodiment of the implantable lead in cross-section toreveal the shield and a doped jacket layer at the shield.

FIG. 14D shows the embodiment of the implantable lead with a pluralityof points with the doped jacket layer at the shield.

FIG. 15A shows an embodiment of the implantable lead having a leadanchor coupled to a metal conductor to provide the RF pathway to ground.

FIG. 15B shows the embodiment of the implantable lead in cross-sectionto reveal the shield, the metal conductor, and the lead anchor.

FIG. 15C shows an embodiment of the implantable lead having a leadanchor coupled directly to the shield to provide the RF pathway toground.

FIG. 15D shows the embodiment of the implantable lead in cross-sectionto reveal the shield and the lead anchor.

FIG. 15E shows an embodiment of the implantable lead having a leadanchor with a non-conductive coating.

FIG. 16 shows an embodiment of an implantable medical system thatincludes an implantable medical device (IMD) coupled to an extensioncontaining a shield which is coupled to a lead containing a shield.

FIG. 17A shows an embodiment of an implantable extension coupled to animplantable lead with the shield of each revealed.

FIG. 17B shows an embodiment of a coupling of the implantable lead andextension in cross-section to reveal the shield, shield electrode, andfilars of the lead and a shield connector and jumper wire of the leadextension.

FIG. 17C shows an embodiment of a coupling of the implantable lead andextension in cross-section to reveal the shield, shield electrode, andfilars of the lead and a shield connector and shield of the leadextension.

FIG. 17D shows an embodiment of a coupling of the implantable lead andextension in cross-section to reveal the filars, filar jumper, and filarelectrode of the lead and a filar connector, filar jumper wire, andshield jumper wire of the lead extension.

FIG. 17E shows an embodiment of a coupling of the implantable lead andextension in cross-section to reveal the filars, filar jumper wire, andfilar electrode of the lead and a filar connector, filar jumper wire andshield of the lead extension.

FIG. 17F shows an embodiment of an implantable extension coupled to animplantable lead where a jumper wire interconnects the two shields.

FIG. 17G shows an embodiment of an implantable extension coupled to animplantable lead where the shield of the extension extends to the shieldconnector of the extension to interconnect the two shields.

FIG. 18 shows an embodiment of an implantable medical system thatincludes an implantable medical device (IMD) coupled to a leadcontaining a shield.

FIG. 19A shows an embodiment of an implantable lead with the shieldrevealed.

FIG. 19B shows the embodiment of the implantable lead in cross-sectionto reveal the shield and filars.

FIG. 20 shows an embodiment of the implantable lead where the shieldterminates at a butt joint to an insulation extension.

FIG. 21 shows an embodiment of the implantable lead where the shieldterminates at a scarf joint to an insulation extension.

FIG. 22 shows one example of a set of steps to create the implantablelead of FIGS. 20 and 21.

FIG. 23 shows an embodiment of the implantable medical lead where theshield terminates at a lap joint to an insulation extension.

FIG. 24 shows one example of a set of steps to create the implantablelead of FIG. 23.

FIG. 25 shows an embodiment of the implantable medical lead where theshield terminates at a ring within a lap joint.

FIG. 26 shows an embodiment of the implantable medical lead where theshield terminates at a ring at a butt joint.

FIG. 27 shows an embodiment of the implantable medical lead where wiresof the shield fold over individually at the termination point.

FIG. 28 shows an embodiment of the implantable medical lead where ajoint at the shield termination includes a barbed connection to an innerinsulation layer.

FIG. 29 shows an embodiment of the implantable medical lead where ajoint at the shield termination includes a barbed connection to an innerinsulation layer.

FIG. 30 shows an embodiment of an implantable medical system thatincludes an implantable medical device (IMD) coupled to a leadcontaining a shield.

FIG. 31A shows an embodiment of an implantable lead with the shieldrevealed.

FIG. 31B shows the embodiment of the implantable lead in cross-sectionto reveal the shield and filars.

FIG. 32 shows an embodiment of the implantable lead where the shieldterminates to a metal connector near a butt joint to an insulationextension.

FIG. 33 shows an embodiment of the implantable lead where the shieldterminates to a metal connector near a scarf joint to an insulationextension.

FIG. 34 shows one example of a set of steps to create the implantablelead of FIGS. 32 and 33.

FIG. 35 shows an embodiment of the implantable medical lead where theshield terminates to a metal connector near a lap joint to an insulationextension.

FIG. 36 shows one example of a set of steps to create the implantablelead of FIG. 35.

FIG. 37 shows an embodiment of the implantable medical lead where theshield terminates between a pair of metal connectors near a joint to aninsulation extension.

FIG. 38 shows an alternative embodiment where a top metal connector ofthe pair has sharp features to penetrate an outer insulation layer.

FIG. 39 shows an embodiment of the implantable medical lead where theshield terminates between a pair of metal connectors near a lap joint toan insulation extension.

FIG. 40 shows an alternative embodiment of the implantable medical leadwhere an inner metal connector is mounted flush with an inner insulationlayer.

FIG. 41 shows one example of a set of steps to create the implantablelead of FIGS. 37-40.

FIG. 42 shows an embodiment of the implantable medical lead where theshield folds over to terminate between a pair of metal connectors near ajoint to an insulation extension.

FIG. 43 shows one example of a set of steps to create the implantablelead of FIG. 42.

FIG. 44 shows an embodiment of the implantable medical lead where theshield laps onto a metal connector near a joint to an insulationextension.

FIG. 45 shows one example of a set of steps to create the implantablelead of FIG. 44.

FIG. 46 shows an embodiment of the implantable medical lead where theshield exits the insulation layers at a taper and terminates between apair of metal connectors.

FIG. 47 shows one example of a set of steps to create the implantablelead of FIG. 46.

FIG. 48 shows an embodiment of the implantable medical lead where wiresof the shield fold over individually at the termination point at a metalconnector.

FIG. 49 shows a percutaneous implantation scenario of an embodiment ofan implantable medical lead.

FIG. 50 shows an implantable medical system configuration resulting fromthe percutaneous implantation of FIG. 49.

FIG. 51 shows an embodiment of the implantable medical lead that has abraided metal shield providing torsional stiffness.

FIG. 52 shows a cross-section of an embodiment of the implantablemedical lead where no rotational coupling exists to the stylet.

FIG. 53 shows a cross-section of an embodiment of the implantablemedical lead where a square-shaped rotational coupling exists to thestylet.

FIG. 54 shows a cross-section of an embodiment of the implantablemedical lead where a star-shaped rotational coupling exists to thestylet.

FIG. 55 shows a cross-section of an embodiment of the implantablemedical lead where a hexagonal-shaped rotational coupling exists to thestylet.

FIG. 56 shows a proximal end of an embodiment of the implantable medicallead achieving a rotational coupling with a tapered feature of a stylethub.

FIG. 57 shows a proximal end of an embodiment of the implantable medicallead achieving a rotational coupling with a splined feature of a stylethub.

FIG. 58 shows a proximal end of an embodiment of the implantable medicallead achieving a rotational coupling with a threaded feature of a stylethub.

FIG. 59 shows an embodiment of an implantable medical system includingan IMD and two leads, each with a radiopaque marker sutured to the lead.

FIG. 60 shows an embodiment of an implantable medical system includingan IMD and a lead, with a radiopaque marker sutured to the IMD case.

FIG. 61 shows an embodiment of an implantable medical system includingan IMD and a lead, with a radiopaque marker placed loosely in a pocketnearby the IMD and lead.

FIG. 62 shows an embodiment of an implantable medical system includingan IMD and a lead, with a radiopaque marker glued to the lead.

FIG. 63 shows an embodiment of an implantable medical system includingan IMD and a lead, with a radiopaque marker glued to the IMD case.

FIG. 64 shows an embodiment of an implantable medical system includingan IMD and a lead, with a radiopaque marker clamped to the lead.

FIG. 65 shows an embodiment of an implantable medical system includingan IMD and a lead, with a radiopaque marker clamped to the IMD case.

FIG. 66 shows an embodiment of an implantable medical system includingan IMD and a lead, with a radiopaque marker crimped to the lead.

FIG. 67A shows an embodiment of an implantable medical system includinga lead and a radiopaque coil being placed onto the lead in a radiallyexpanded state.

FIG. 67B shows an embodiment of an implantable medical system includinga lead and a radiopaque coil once placed onto the lead in a radiallycontracted state.

FIG. 68A shows the coil on an installation tool in the radially expandedstate prior to placement on the lead.

FIG. 68B shows the coil being placed onto the lead from the tool toachieve the radially contracted state.

FIG. 69A shows an embodiment of a polymer structure that fits axiallyonto the lead and provides a radiopaque plate.

FIG. 69B shows an embodiment of an implantable medical system where thepolymer structure of FIG. 69A is positioned on the lead.

FIG. 69C shows an embodiment of an implantable medical system where anembodiment of a polymer structure that has an anchor format includingsuture wings and a radiopaque plate is sutured in place on the lead.

FIG. 70A shows an embodiment of a polymer structure that fits axiallyonto the lead and provides a radiopaque coil.

FIG. 70B shows an embodiment of an implantable medical system where thepolymer structure of FIG. 70A is positioned on the lead.

FIG. 70C shows an embodiment of an implantable medical system where anembodiment of a polymer structure that has an anchor format includingsuture wings and a radiopaque coil is sutured in position on the lead.

FIG. 71 shows an embodiment of the lead that includes a shield toprovide safety during medical procedures such as an MRI scan.

FIG. 72 shows the embodiment of FIG. 71 in cross-section to reveal theshield, filars, and lumen.

FIG. 73 shows an embodiment of an implantable medical system thatincludes an implantable medical device (IMD) coupled to a leadcontaining a shield.

FIG. 74A shows an embodiment of an implantable lead with the shieldrevealed.

FIG. 74B shows an embodiment of an implantable lead with the shieldhaving an axial cut that creates a slot.

FIG. 74C shows an embodiment of an implantable lead with the shieldhaving the axial cut but with the edges of the slot brought into anoverlapping configuration to close the slot.

FIG. 74D shows an embodiment of an implantable lead with the shieldhaving the axial cut but with a shield patch applied across the slot.

FIG. 75A shows the embodiment of the implantable lead of FIG. 74A incross-section to reveal the shield and filars.

FIG. 75B shows the embodiment of the implantable lead of FIG. 74B incross-section to reveal the shield and the slot.

FIG. 75C shows the embodiment of the implantable lead of FIG. 74C incross-section to reveal the shield having the overlapping edges.

FIG. 75D shows the embodiment of the implantable lead of FIG. 74D incross-section to reveal the shield and the shield patch.

FIG. 76A shows an embodiment of the shield as an equivalent tube toreveal a linear axial cut that produces a linear slot.

FIG. 76B shows the embodiment of the shield as an equivalent tube toreveal the edges of the slot that overlap to close the slot.

FIG. 76C shows the embodiment of the shield as an equivalent tube toreveal the shield patch that closes the slot.

FIG. 76D shows an embodiment of the shield as an equivalent tube toreveal a helical axial cut forming a helical slot.

FIG. 77 shows an embodiment of an implantable medical system thatincludes an implantable medical device (IMD) coupled to a leadcontaining a shield.

FIG. 78A shows an embodiment of an implantable lead with the shieldrevealed.

FIG. 78B shows the embodiment of the implantable lead of FIG. 78A incross-section to reveal the shield and filars.

FIG. 79A shows one embodiment of a guard at the termination of theshield.

FIG. 79B shows another embodiment of a guard at the termination of theshield.

FIG. 79C shows another embodiment of a guard at the termination of theshield.

FIG. 80A shows the embodiment of FIG. 79A in cross-section to revealfirst and second portions of the continuous shield forming a guard atthe termination of the shield.

FIG. 80B shows the embodiment of FIG. 79B in cross-section to revealfirst and second portions of the two-piece shield forming a guard at thetermination of the shield.

FIG. 80C shows the embodiment of FIG. 79C in cross-section to reveal afirst portion including first and second sub-portions and a secondportion at the termination of the two-piece shield.

DETAILED DESCRIPTION

Embodiments of implantable medical leads that include shields aredisclosed herein. Ten primary subject matter topics are presented, whereeach new topic begins with reference to FIGS. 1, 3, 11, 16, 18, 30, 49,59, 73, and 77. However, this detailed description should be read as awhole whereby subject matter of embodiments corresponding to oneparticular topic is applicable to embodiments corresponding to othertopics.

For instance, shield details disclosed in relation to FIGS. 1-2H arealso applicable to the shields of all embodiments disclosed in FIGS.3-80C where such shield details may be desired. The examples ofgrounding a shield within a lead as disclosed in relation to FIGS. 3-15Eare applicable to all embodiments disclosed herein where a groundedshield may be desired. The examples of shielding the extension andinterconnecting the shielding of the lead to the extension as disclosedin relation to FIGS. 16-17G are applicable to all embodiments disclosedherein where inclusion of a shielded extension may be desired. Theexamples of terminating the shield as disclosed in relation to FIGS.18-48 are applicable to all embodiments disclosed herein whereterminating the shield within the lead body may be desired. The examplesof rotationally coupling the lead body to a stylet as disclosed inrelation to FIGS. 49-58 are applicable to all embodiments disclosedherein where such rotational coupling may be desired. The examples ofmarkers for the lead as disclosed in relation to FIGS. 59-72 areapplicable to all embodiments disclosed herein where such a marker maybe desired. The examples of breaking the circumferential mechanicalcontinuity of the shield as disclosed in FIGS. 73-76D are applicable toall embodiments disclosed herein where such a lack of continuity may bedesired. The examples of guarding the termination of the shield asdisclosed in FIGS. 77-80C are applicable to all embodiments disclosedherein where a guarded shield termination may be desired.

Embodiments disclosed in relation to FIGS. 1-2H provide for radiofrequency (RF) shielding of an implantable lead that may be connected toan implantable medical device (IMD). A shield is present within thejacket of the implantable lead. The shield is designed to provide RFshielding while also providing various mechanical properties suitablefor implantation.

FIG. 1 shows an example of an implantable medical system 1100 thatincludes an IMD 1102 coupled to a lead 1108. The IMD 1102 includes ametal can 1104, typically constructed of a medical grade titanium, suchas grades 1-4, 5 or 9 titanium, or similar other biocompatiblematerials. The IMD 1102 includes a header 1106 typically constructed ofmaterials such as polysulfone or polyurethane, that is affixed to themetal can 1104. The header 1106 is shown transparently for purposes ofillustration. The header 1106 provides a structure for securing the lead1108 to the IMD 1102 and for establishing electrical connectivitybetween circuitry of the IMD 1102 and electrodes of the lead 1108.

The lead 1108 includes electrodes 1116 on a distal end that arepositioned at a stimulation site within a patient. The lead alsoincludes connector rings 1110 on a proximal end that is positionedwithin the header 1106. The connector rings 1110 make physical contactwith electrical connections 1111 within the header. The electricalconnections 1111 may include a metal contact that the connector ring1110 rests against upon being inserted into the header 1106 where a wireextends from the metal contact into the can 1104 where the circuitry ishoused. Signals applied by the IMD 1102 to the connector rings 1110 areconducted through the lead 1108 to the electrodes 1116 to provide thestimulation therapy to the patient.

The lead 1108 is secured in the header 1106 such as by a set screw block1112 within the header 1106 that allows at least one set screw 1114 tobe tightened against at least one of the connector rings 1110. A shield1118 such as the one discussed below with reference to FIGS. 2A and 2Bis located within the lead 1108. The shield 1118 may or may not begrounded to the metal can 1104 at the IMD 1102 of FIG. 1 or at variouspoints along the length of the lead. The shield 1118 may or may not begrounded through other mechanisms as well. For instance, the shield 1118may be located within the lead 1108 at a small distance from the surfaceso that the shield 1118 will effectively capacitively couple to thetissue along the length of the lead to dissipate energy to the tissueover the length.

FIGS. 2A and 2B show an example of the lead 1108, where a shield 1118 ispresent. An outer jacket layer 1120 is shown transparently in FIG. 2Afor purposes of illustrating the shield 1118. The shield 1118 blocks atleast some RF energy from directly coupling to conductive filars 1124that are present within the lead 1108. The conductive filars 1124 extendthe length of the lead and interconnect the proximal connector rings1110 to the distal electrodes 1116 so that stimulation signals areconducted from the proximal end to the distal end of the lead 1108.

As shown in FIG. 2A, the shield 1118 of this example is a braided metalwire. The metal wire may be constructed of various materials such astitanium, tantalum, niobium, platinum-iridium alloy, platinum,palladium, gold, stainless steel, and their alloys, or other metals. Themetal braid wire may be a biocompatible metal, particularly forembodiments where a portion of the shield 1118 may be exposed forpurposes of grounding. Biocompatible metals ensure that if the shield1118 is exposed to tissue, either by design or due to wear on the lead1108, the shield 1118 does not become a toxin to the patient.

As shown in FIG. 2B, the shield 1118 may be embedded within the jacketof the lead 1108. One manner of constructing the lead 1108 with theshield 1118 is to provide a jacket that includes an inner layer ofinsulation 1122 that isolates an inner region 1121 where the filars 1124and any additional insulation layer 1126, such aspolytetrafluoroethylene (PTFE) that may surround each filar 1124 arelocated. According to some embodiments, this inner layer 1122 may have apost-assembly thickness 1130 of at least 2 mils and may be significantlylarger such as 5 or 6 mils depending upon size constraints for the lead1108 and/or the size of the outer layer 1120. The shield 1118 may thenreside on the outer portion of the inner layer 1122, and the jacket'souter layer of insulation 1120 may then enclose the shield 1118. Theouter layer 1120 provides an overall lead diameter 1134. The outerjacket 1120 maybe added over the braid 1118, or it may be extruded overthe braid.

For embodiments where it is desirable for the shield 1118 to RF coupleto tissue, typically as capacitive coupling, either as an alternative togrounding at the can of the IMD or specific points along the length orin addition to grounding at the can or along the length, the entireouter jacket layer 1120 may be relatively thin, particularly for theportion passing over the braid wires of the shield 1118. According tothe various embodiments a post-assembly thickness 1132 for the portionof the outer layer 1120 passing over a single braid wire may be on theorder of 0.5 to 5 mils. The thickness of the outer layer 1120 over theshield 1118 is reduced by a braid wire diameter at points where braidwires intersect. Accordingly, the post-assembly thickness 1132 over thesingle wire may vary depending upon a chosen braid wire diameter so thatadequate coverage also exists at the intersection points. Furthermorethe thickness may be less than 0.5 mils, particularly where tissuein-growth is not of concern and in that case the outer layer 1120 couldbe omitted.

This thickness of the outer layer 1120 over the braid wires may alsovary depending upon the type of metal used for the braid wires. Forinstance, it has been found that the thickness of the outer layer 1120has less of an impact on the heating at the electrode when using atitanium braid wire than when using a tantalum wire with all else beingequal. However, with an outer layer 1120 whose post-assembled thickness1132 is on the lower side of the range, such as 2 mils or less, tantalumbraid wires may allow for less heating at the electrodes than iftitanium braid wires are used.

Where the shield 1118 grounds at the can 1104 and/or at one or morespecific locations along its length, via a direct current coupling or acapacitive coupling, the shield 1118 may be located further from theouter surface of the lead 1108. This increased depth of the shield 1118within the jacket may provide for a more durable lead 1108 in terms ofprotecting the braid wires in areas of high flexure and motion, such asin the lumbar spine.

The inner and outer jackets 1122, 1120 may be constructed of the same orsimilar materials such as various flexible polymers, examples of whichare polyurethanes and silicones. Biocompatible materials may be used,especially for the outer layer 1120 when the outer layer 1120 has directcontact with body tissue. A lumen 1128 may be included in an innerregion 1121, particularly for percutaneous leads 1108, to allow a styletto be inserted for purposes of pushing and steering the lead into thedesired position within the patient. For leads where an inner region1121 is filled to define the lumen 1128, such as where filars 1124 arecables rather than the coils as shown, this inner region 1121 may beconstructed of materials such as polyurethanes, silicones,polyetheretherketone (PEEK), nylon or other biocompatible polymermaterial.

FIG. 2C shows a view of the implantable lead 1108 where variousparameters related to the braid wires can be seen. The inner layer ofinsulation 1122, as well as the outer layer 1120, defines an axialdimension 1136 that runs along the length of the lead 1108. Braid wiressuch as braid wires 1140, 1142 are braided around the inner layer 1122.A first set of braid wires including braid wire 1140 is wound around theinner layer 1122 in a first direction while a second set of braid wiresincluding braid wire 1142 is wound around the inner layer 1122 in asecond direction that is opposite the first. The braid wires of thefirst set and the braid wires of the second set weave together duringthe braiding with a braid wire of the first set passing over some wiresand under others of the second set in a repeating pattern.

The weaving may use a particular pattern, such as passing over one,passing under one, passing over one, and so on or such as passing overtwo, passing under two, passing over two, and so on. With wires oflarger diameter, or where wires are used in pairs, then a pattern oftwo-over-two-under helps reduce the stress on the wire as it weaves backand forth. If the wires are small and single, with a relatively largeaperture between braid wires, then one-over-one-under works well. Thewire stress is a factor to consider because implant leads flexcontinually with body motion and typically are expected to last manyyears.

The braiding has various parameters of interest. A first parameter isthe braid angle 1144. Here, the braid angle 1144 is defined as the angleof the braid wire as measured transversely from the axial dimension1136; however, others sometimes define it relative to the axis of thelead. So, as shown in FIG. 2C, the braid angle 1144 is measured betweenthe braid wire and the transverse dimension 1138. According to variousembodiments, the braid angle measured in this way is less than 60degrees.

This braid angle 1144 has several implications. The braid angle 1144 isone factor in setting the maximum dimension of the braid aperture 1141shown in FIG. 2C, and hence the degree of coverage formed by the braidwires. This braid angle 1144 is also a factor in relation to the degreeof stiffness of the lead in flexure and the tendency of the braid wiresto break during flexure. The braid angle is also a factor in thecohesion of the outer layer of insulation 1120 to the inner layer ofinsulation 1122, because when the aperture is of adequate size, cohesionoccurs between the two layers 1120, 1122 through the aperture.

Another parameter of interest as shown in FIG. 2C is the axial spacing1146 between adjacent wires of a set. According to various embodiments,the axial spacing 1146 has an upper limit equal to the lead diameter1134. The axial spacing 1146 is also a factor in the aperture size, theaxial stiffness, the bending stiffness, and the kink resistance.

Another parameter of interest, which is related to the braid angle 1144and the axial spacing 1146, is the number of wires in each set.According to various embodiments, the first set of braid wires which arewound in the first direction includes at least three braid wires.Likewise, the second set of braid wires which are wound in the seconddirection includes at least three braid wires. These two sets of atleast three braid wires each ensures that for the various ranges ofparameters disclosed herein, the aperture 1141 has a transversedimension that is sufficiently small to effectively shield the RF energyin the MRI spectrum, which typically spans from 43 MHz to 128 MHz.

The total number of braid wires is limited by the allowable axial andbend stiffness for the braid angle and braid wire size. In someexamples, there may be as many as 16 braid wires in each set for a totalof 32 braid wires. However, as shown in the example of FIG. 2C, each setincludes six braid wires, where braid wire 1140 reappears on a givenside of the lead 1108 after five other braid wires are wound. Likewise,braid wire 1142 reappears on the side of the lead 1108 after five otherbraid wires are wound.

FIG. 2D shows another lead embodiment 1150 that demonstrates anotherbraid wire parameter of interest. In this example, the braid wires arepaired so that two braid wires that are in contact wind around the innerlayer 1122 instead of a single wire. For instance, dual braid wires 1152and 1154 of a first set wound in a first direction are in contact aseach winds around the inner layer 1122. Dual braid wires 1156 and 1158of a second set wound in a second direction are in contact as each windsaround the inner layer 1122.

The braid wires bundled together in this manner affect the stiffness ofthe lead 1108 as well as the aperture size. Bundling braid wires in thismanner may provide coverage like that of wider dimensioned braid wires,such as rectangular braid wires, but without the increased bendingstresses associated with the corners present on the rectangular braidwire.

FIG. 2E is an enlarged view of a portion of a lead 1108 to illustratethe cross-section of the braid wires. The view is a cross-section wherethe cut through the lead 1108 is taken at an angle perpendicular to thedirection of travel of the topmost braid wire 1142 so as to provide atrue cross-section of the topmost braid wire 1142. Here the topmostbraid wire 1142 has a round cross-section and provides a braid wirediameter 1148. According to various embodiments, the braid wire diameterranges from about 0.5 mils to about 2.5 mils. The braid wire diameter ismeasured as the dimension that faces outward from the inner layer 1122as shown in FIG. 2E. The round cross-section lacks corners that mayotherwise affect the bend stiffness of the lead 1108, but the roundcross-section provides less coverage than other cross-sectional shapesthat have a same height extending into the outer layer 1120 from theinner layer 1122.

FIG. 2F is an enlarged view of a portion of a lead 1160 to illustratethe cross-section of the braid wires. As in FIG. 2E, the view is across-section where the cut through the lead 1160 is taken at an angleperpendicular to the direction of travel of the topmost braid wire 1162so as to provide a true cross-section of the topmost braid wire 1162.Here the braid wire 1162 has a rectangular cross-section and provides abraid wire width 1168. According to various embodiments, the braid wirewidth ranges from about 2 mils to about 5 mils. The braid wire width ismeasured as the dimension that faces outward from the inner layer 1164as shown in FIG. 2F. The rectangular cross-section has corners that mayaffect the bend stiffness of the lead 1108 but provides more coveragethan a round cross-sectional shape that has a same height extending intoan outer layer 1166 from the inner layer 1164.

FIG. 2G is an enlarged view of a portion of a lead 1170 to illustratethe cross-section of the braid wires. As in FIG. 2E, the view is across-section where the cut through the lead 1170 is taken at an angleperpendicular to the direction of travel of the topmost braid wire 1172so as to provide a true cross-section of the topmost braid wire 1172.Here the topmost braid wire 1172 has an oval cross-section and providesa braid wire major axis diameter 1178. According to various embodiments,the braid wire major axis diameter ranges from about 0.5 mils to about 4mils. The braid wire major axis diameter is measured as the dimensionthat faces outward from the inner layer 1176 as shown in FIG. 2G. Theoval cross-section lacks corners that may affect the bend stiffness ofthe lead 1108 but provides coverage similar to a rectangularcross-section that has a same height extending into an outer layer 1174from the inner layer 1176.

In each of the examples of FIGS. 2E-2G, regardless of thecross-sectional shape and the material used, the braid wires have anultimate tensile strength satisfactory for implantation. According tothe various embodiments, this ultimate tensile strength is at least150,000 pounds per square inch (150 ksi).

FIG. 2H shows the lead 1108 from end to end with the shield 1118 in viewto illustrate the termination of the shield 1118 at the proximal end1105 and the distal end 1107. The shield 1118 terminates prior toreaching the most distal connector 1109 of the proximal end 1105 andprior to reaching the most proximal electrode 1116 of the distal end1107. Terminating the shield 1118 at a distance 1117 from the connector1109 and at a distance 1119 from the electrode 1116 reduces thelikelihood of RF energy that radiates from the end of the shield,leaking from the shield onto the conductor filars and then to theconnector 1109 and/or electrode 1116. However, the shield terminationdistances 1117, 1119 are not too large so that adequate coverage overthe filars 1124 is maintained.

The shield termination distance from the distal electrodes and proximalconnectors may vary. According to the various embodiments, the distancemay range from about 0.5 millimeters to about 10 centimeters dependingupon the location of the lead 1108. For instance, if the distal tip islocated in the brain or spinal column where intensities of RF energy arelower, then distance from the end of the shield 1118 to the nearest edgeof the distal electrode may be from 0.5 mm up to about 10 cm, or fromabout 2 mm to 2 cm to further reduce electrode coupling and filarexposure. However, in other locations where the entire lead 1108 is justunder the skin as for peripheral nerve stimulation, the distance fromthe end of the shield 1118 to the nearest edge of the distal electrodemay be less than about 2 cm to prevent overexposure of the filars 1124.In these cases, the distance may be on the order of 2 mm or more toensure that excessive RF coupling from the shield 1118 to the electrodesis avoided.

In one particular example, the lead 1108 is provided with a shield 1118where the total lead diameter is 53.6 mils. The inner insulation layer1122 has an as assembled inside diameter of 35 mils and an as assembledoutside diameter of 50.19 mils for a total thickness of 5.89 mils or5.39 mils to the inner edge of the braid wire. The outside insulationlayer 1120 has an as assembled outside diameter of 53.6 mils and a totalthickness of 3.41 mils, with 1.41 mils of thickness existing over braidwire intersection points and while the thickness over a single braidwire approaches 2.66 mils as the single braid wires approaches anintersection point where the single braid wire will pass under anintersecting braid wire. The braid wire is round in cross-section with adiameter of 1.25 mils and being embedded by about 0.5 mils into theinner layer 1122. Two sets of eight braid wires are provided for a totalof sixteen braid wires, with the braid wires establishing a braid angleof 22 degrees with an axial spacing between adjacent braid wires of 7.5mils. The shield 1118 terminates about 2 mm from the nearest edge of thedistal electrode and proximal connector.

In another particular example, the lead 108 is provided with thespecifications described in the preceding paragraph except that theshield gaps and depth the shield sinks into the inner insulation layer1122 are different. Here, the shield 1118 terminates about 1 mm from thenearest edge of the distal electrode and proximal connector and theshield sinks 0.25 mil. As a result, the inner insulation thickness tothe inner edge of the braid wire is 5.6 mils.

In another particular example, the lead 108 is provided with thespecifications described in the preceding paragraph except insulationthicknesses, braid angle, and proximal shield gaps differ. In thisexample, the braid depth from the outer surface of the outer layer 1120to the outer edge of a braid wire is about 2 mils at braid wireintersection points while the thickness over the braid wire approaches3.25 mils as the single braid wire approaches an intersection pointwhere the braid wire passes under an intersecting braid wire. The innerinsulation layer 122 has an average thickness of 4.5 mils to the inneredge of the braid wire while the braid wire sinks into the innerinsulation layer 1122 by about 0.25 mil. The shield 1118 terminatesabout 1.27 mm from the nearest edge of the distal electrode andterminates about 10 mm from the nearest edge of the proximal connector.The braid angle is about 23 degrees.

Embodiments disclosed in relation to FIGS. 3-10C provide for radiofrequency (RF) grounding of a shield present within an implantable lead.The shield may be grounded in various ways such as to a can of animplantable medical device (IMD) or to a ground plate on a header of theIMD. The pathway for grounding may be a direct current pathway or becapacitively coupled. The pathway for grounding the shield may couple tothe shield at a point along the lead that is external to the header ofthe IMD or may couple to the shield at a point within the header.

FIG. 3 shows an example of an implantable medical system 2100 thatincludes an IMD 2102 coupled to a lead 2108. The IMD 2102 includes ametal can 2104, typically constructed of a medical grade titanium, suchas grades 1-4, 5 or 9 titanium, or similar other biocompatiblematerials. The IMD 2102 includes a header 2106 typically constructed ofmaterials such as polysulfone or polyurethane, that is affixed to themetal can 2104. The header 2106 is shown transparently for purposes ofillustration. The header 2106 provides a structure for securing the lead2108 to the IMD 2102 and for establishing electrical connectivitybetween circuitry of the IMD 2102 and electrodes of the lead 2108.

The lead 2108 includes electrodes 2116 on a proximal end that arepositioned at a stimulation site within a patient. The lead alsoincludes connector rings 2110 on a proximal end that is positionedwithin the header 2106. The connectors 2110 make physical contact withelectrical connections 2111 within the header. The electricalconnections 2111 may include a metal contact that the electrode 2110rests against upon being inserted into the header 2106 where a wireextends from the metal contact into the can 2104 where the circuitry ishoused. Signals applied by the IMD 2102 to the electrodes 2110 areconducted through the lead 2108 to the electrodes 2116 to provide thestimulation therapy to the patient.

The lead 2108 is secured in the header 2106 such as by a set screw block2112 within the header 2106 that allows at least one set screw 2114 tobe tightened against at least one of the connectors 2110. The shield2118 may be grounded by metal contacts provided along the lead toestablish a ground pathway from the shield 2118 to the tissue. Asanother option, the shield 2118 may be located within the lead 2108 at asmall distance from the surface so that the shield 2118 will effectivelycapacitively couple to the tissue along the length of the lead todissipate energy to the tissue over the length.

FIGS. 4A and 4B show an example of the lead 2108, where a shield 2118 ispresent. An outer jacket layer 2120 is shown transparently in FIG. 4Afor purposes of illustrating the shield 2118. The shield 2118 blocks atleast some RF energy from directly coupling to conductive filars 2124that are present within the lead 2108. The conductive filars 2124 extendthe length of the lead and interconnect the proximal connectors 2110 tothe distal electrodes 2116 so that stimulation signals are conductedfrom the proximal end to the distal end of the lead 2108.

As shown in FIG. 4A, the shield 2118 of this example is a braided metalwire. The metal wire may be constructed of various materials such astitanium, tantalum, niobium, platinum-iridium alloy, platinum,palladium, gold, stainless steel, and their alloys, or other metals. Itmay be desired to utilize a biocompatible metal for the shield 2118,particularly for embodiments where a portion of the shield 2118 may beexposed for purposes of grounding. While the shield 2118 is shown as abraid, other shield configurations may be chosen particularly whereflexibility is not an issue such as a foil strip wrapped about the lead2108 in an overlapping manner or an outer layer 2120 that is heavilydoped with conductive particles.

As shown in FIG. 4B, the shield 2118 may be embedded within the jacketof the lead 2108. One manner of constructing the lead 2108 with theshield 2118 is to provide an inner jacket 2122 that encloses the filars2124 and any additional insulation layer 2126, such aspolytetrafluoroethylene (PTFE) that may surround each filar 2124. Theshield 2118 may then reside on the outer portion of the inner jacket2122, and the outer jacket 2120 may then enclose the shield 2118. Theouter jacket 2120 maybe added over the braid 2118, or it may be extrudedover the braid.

For embodiments where it is desirable for the shield 2118 to RF coupleto tissue, typically as a capacitive coupling, either as an alternativeto grounding at the can of the IMD or in addition to grounding at thecan, the amount of the outer jacket layer 2120 covering the shield 2118may be relatively thin, such as on the order of 0.5 to 5 mils. Where theshield 2118 grounds at the can of the IMD and grounding via a capacitivecoupling from the shield through the outer jacket 2120 directly to thetissue is of less significance, then the shield 2118 may be locatedfurther from the outer surface of the lead 2108.

The inner and outer jackets 2122, 2120 may be constructed of the same orsimilar materials such as various flexible and biocompatible polymers,examples of which are polyurethanes, and silicones. A lumen 2128 may bepresent inside of the inner jacket 2122 around which the insulatedfilars 2124 are coiled or otherwise positioned. The lumen 2128 may beuseful, particularly for percutaneous leads 2108, to allow a stylet tobe inserted for purposes of pushing and steering the lead 2108 into thedesired position within the patient.

FIG. 4C shows one example of exposing the shield 2118 for purposes ofgrounding the shield 2118. In this example, the outer layer 2120 of thejacket has been removed at first point along the lead 2108 near theproximal end to expose the shield 2118 and the inner jacket 2122. Forexample, an excimer laser may be used to ablate the outer layer 2120.Physical contact may then be established between the shield 2118 and anelectrode attached to the lead, a spring loaded connector or a connectorblock, a wire, or other direct current or capacitive coupling. Forinstance, a ground wire could be adhesively bonded with glue or tape incontact with the exposed shield 2118. Depending upon the embodiment,this first point along the lead where the shield 2118 is exposed may belocated either inside or outside of the header of the IMD. Furthermore,depending upon the embodiment the coupling to the exposed shield 2118may be a direct current coupling or a capacitive coupling, eitherproviding a pathway for RF current to pass to ground.

FIG. 4D shows another example of providing a pathway to ground theshield 2118. Here, an electrode 2130 is attached at the first pointalong the lead 2108 near the proximal end to provide a robust physicalconnection to a spring loaded connector, a connector block, a wire, orother direct current or capacitive coupling. Depending upon theembodiment, this first point along the lead where the electrode 2130 ispositioned may be located either inside or outside of the header of theIMD. Furthermore, depending upon the embodiment a coupling to theelectrode 2130 may be a direct current coupling or a capacitivecoupling, either providing a pathway for RF current to pass to ground.

FIGS. 5A-5C show embodiments of grounding the shield to the can of theIMD by using a connector block mounted on the IMD and coupling agrounding path to the shield outside of a header of the IMD. Theimplantable medical system 2150 includes an IMD 2152 having a metal can2154 and a header 2156. One or more leads 2164 extend from the headerand pass through a connector block 2158 that is mounted to the can 2154.

The connector block 2158 includes features to ground the shield of thelead 2164 to the can 2154, such as a connector 2160 and a can attachment2162. For instance, the connector block 2158 may be constructed of abiocompatible plastic or other non-conductor while the connector 2160provides conduction to the can attachment 2162. The can attachment 2162may be of various forms. For example, a wire that extends from theconnector 2160 to the can 2154 where the can attachment 2162 is weldedor otherwise affixed to the can 2154. As another example, the connectorblock 2158 may include a metal plate that contacts the metal can 2154via a weld or other attachment.

FIG. 5B is a side view showing a pair of pass-through features of theconnector block 2158 and a pair of leads 2164 having shields to begrounded. The connector block 2158 is shown in a cross-section so that aset screw 2168 is visible. The electrode or other contact for the shieldof the lead 2164 is positioned within the pass-through 2166 such thatthe set screw 2168 and the electrode or other contact for the shield arealigned. The set screw 2168 is tightened against the electrode or othercontact to establish the ground to the can 2154. The pass-through 2166may be a slot through the connector block 2158 so that the lead 2164 canbe lowered into the slot. As another option, the pass-through 2166 maybe a bore through the connector block 2158 and the lead 2164 is fedthrough the bore.

FIG. 5C is a side view showing a pair of pass-through features ofanother embodiment of the connector block 2158 and a pair of leads 2164having shields to be grounded. The connector block 2158 includes springloaded connectors 2172. The electrode or other contact for the shield ofthe lead 2164 is positioned within the pass-through 2170 such that thespring loaded connector 2172 and the electrode or other contact for theshield are aligned. The electrode or other contact to the shield isforced within the spring loaded connector 2172 to establish the groundto the can 2154. As with the embodiment of FIG. 5B, the pass-through2170 of this embodiment may be a slot through the connector block 2158so that the lead 2164 can be lowered into the slot or may be a borethrough the connector block 2158 where the lead 2164 is fed through thebore.

FIG. 6 shows one example of a spring loaded connector 2174. The springloaded connector 2174 can open slightly when forced by insertion of thelead 2164 and then is biased back against the electrode or other contactof the lead 2164 once the lead is seated within the spring loadedconnector 2174. Other spring loaded connector designs are alsoapplicable.

FIG. 7A shows an implantable medical system 2180 where the shield of alead 2188 is being grounded to a metal can 2184 of an IMD 2182externally of the header 2186. Here, a direct current pathway is beingprovided between the shield and the metal can 2184. A spring loadedconnector 2192 contacts an electrode 2190 on the lead 2188 where theelectrode 2190 is in contact with the shield. A wire 2194 may be madefrom materials such as titanium, tantalum, platinum, stainless steel,nickel chromium, and alloys, and serves as a ground conductor. This wire2194 is attached to the spring loaded connector 2192 by a weld or otherbond. The wire 2194 extends from the spring loaded connector 2192 to themetal can 2184 where a weld 2196 or other bond such as with glue or tapeattaches the wire 2194 to the metal can 2184.

FIG. 7B shows an implantable medical system 2200 where the shield of alead 2208 is being grounded to a metal can 2204 of an IMD 2202externally of the header 2206. Here, a direct current pathway is alsobeing provided between the shield and the metal can 2204. A metalconnector block 2210 having a set screw 2212 contacts an electrode onthe lead 2208 where the electrode is in contact with the shield. A wire2214 serving as a ground conductor is attached to the connector block2210 by a weld or other bond. The wire 2214 extends from the connectorblock 2212 to the metal can 2204 where glue 2216, such as a conductiveepoxy or carbon filled polymer adhesive, or other bond such as a weld ortape attaches the wire 2214 to the metal can 2204.

FIG. 7C shows an implantable medical system 2220 where the shield of alead 2228 is being grounded to a metal can 2224 of an IMD 2222externally of the header 2226. Here, a direct current pathway is alsobeing provided between the shield and the metal can 2224. A coupling2230 such as a ring electrode is in contact with the shield. A wire 2232serving as a ground conductor is attached to the coupling 2230 by a weldor other bond. The wire 2232 extends from the coupling 2230 to the metalcan 2224 where a crimp connector 2234 or other bond such as a weld ortape attaches the wire 2232 to the metal can 2224.

For the examples of FIGS. 7A-7C, various examples of connecting thegrounding wire to the lead and to the can are disclosed. It will beappreciated that any combination of these and other examples ofconnections of the ground wire may be used to provide the direct currentpathway that ultimately provides an RF ground from the shield to themetal can.

FIG. 8A shows an implantable medical system 2240 where the shield of alead 2248 is being grounded to a metal can 2244 of an IMD 2242externally of the header 2246. Here, a capacitively coupled pathway isbeing provided between the shield and the metal can 2244. A coupling2250 such as a spring loaded connector or a ring electrode contacts thelead 2248 and is in contact with the shield. A wire 2252 serving as aground conductor is attached to the coupling 2250 by a weld or otherbond. The wire 2252 extends from the coupling 2250 to nearby the metalcan 2244 where a piece of tape 2254 or other tab affixed to the can 2244attaches to the wire 2252. The tape 2254, such as double-sided tapes,epoxies, or polymer based adhesive, or other tab holds the wire inproximity to the metal can 2244 to establish a capacitive couplingbetween the wire 2252 and the can 2244.

FIG. 8B shows an implantable medical system 2260 where the shield of alead 2268 is being grounded to a metal can 2264 of an IMD 2262externally of the header 2266. Here, a capacitively coupled pathway isbeing provided between the shield and the metal can 2264. A piece oftape 2270 or other tab contacts the lead 2268 at a point where theshield is present. A wire 2272 serving as a ground conductor is attachedto the tab 2270 and is held nearby the lead 2268 and shield to establisha capacitive coupling between the wire 2272 and the shield. The wire2272 extends from the tab 2270 to the metal can 2264 and is affixed tothe metal can 2264 with a weld 2274 or other bond. FIG. 8C shows animplantable medical system 2280 where the shield of a lead 2288 is beinggrounded to a metal can 2284 of an IMD 2282 externally of the header2286. Here, a capacitively coupled pathway is being provided between theshield and the metal can 2284. A coupling 2290 such as a spring loadedconnector or a ring electrode contacts the lead 2288 and is in contactwith the shield. A wire 2292 serving as a ground conductor is attachedto the coupling 2290 by a weld or other bond and extends from thecoupling 2290 to nearby the metal can 2284. Non-conductive glue oranother non-conductive bond 2294 to the can 2284 is present to adhere tothe wire 2292 and hold the wire in proximity to the metal can 2284 toestablish a capacitive coupling between the wire 2292 and the can 2284.

For the examples of FIGS. 8A-8C, various examples of connecting thegrounding wire to the lead and to the can are disclosed, usingcombinations of direct current couplings and capacitive couplings. Itwill be appreciated that any combination of these and other examples ofdirect current coupling and capacitive coupling connections of theground wire may be used to provide the capacitively coupled pathway thatultimately provides an RF ground from the shield to the metal can.

FIG. 9A shows an implantable medical system 2300 where the shield of alead 2308 is being grounded to a metal can 2304 of an IMD 2302 withinthe header 2306. Proximal electrodes 2310 of the lead 2308 areelectrically connected via wires 2312 to the IMD 2302. Here, a directcurrent coupled pathway is being provided between the shield and themetal can 2304. A coupling 2314 such as a spring loaded connector or aring electrode contacts the lead 2308 and is in contact with the shield.A set screw 2316 may be present to further hold the proximal end of thelead 2308 in place within the header 2306. A wire 2318 serving as aground conductor is attached to the coupling 2314 by a weld or otherbond and extends from the coupling 2314 to the metal can 2304 where aweld 2320 or other bond holds the wire 2318 to the can 2304.

FIG. 9B shows an implantable medical system 2330 where the shield of alead 2338 is being grounded to a metal can 2334 of an IMD 2332 withinthe header 2336. Proximal electrodes 2340 of the lead 2338 areelectrically connected via wires 2342 to the IMD 2302. Here, a directcurrent coupled pathway is being provided between the shield and themetal can 2334. A coupling 2344 such as a spring loaded connector or aring electrode contacts the lead 2338 and is in contact with the shield.A wire 2346 serving as a ground conductor is attached to the coupling2344 by a weld or other bond and extends from the coupling 2344 to themetal can 2334 where a weld 2348 or other bond holds the wire 2346 tothe can 2334.

FIG. 9C shows an implantable medical system 2350 where the shield of alead 2358 is being grounded to a metal can 2354 of an IMD 2352 withinthe header 2356. Proximal electrodes 2360 of the lead 2358 areelectrically connected via wires 2362 to the IMD 2352. Here, acapacitively coupled pathway is being provided between the shield andthe metal can 2354. A coupling 2364 such as a spring loaded connector ora ring electrode contacts the lead 2358 and is in contact with theshield. A wire 2366 serving as a ground conductor is capacitivelycoupled to the coupling 2364 within the header 2356 by the headerstructure holding the wire in proximity to the coupling 2364. The wire2366 extends from the capacitive coupling to the metal can 2354 where aweld 2368 or other bond holds the wire 2366 to the can 2354.

FIG. 9D shows an implantable medical system 2370 where the shield of alead 2378 is being grounded to a metal can 2374 of an IMD 2372 withinthe header 2376. Proximal electrodes 2380 of the lead 2378 areelectrically connected via wires 2382 to the IMD 2372. Here, acapacitively coupled pathway is being provided between the shield andthe metal can 2374. A coupling 2384 such as a spring loaded connector ora ring electrode contacts the lead 2378 and is in contact with theshield. A wire 2386 serving as a ground conductor is capacitivelycoupled to the coupling 2384 within the header 2376 by the headerstructure holding the wire in proximity to the coupling 2384. The wire2386 extends from the capacitive coupling toward the metal can 2374 andis capacitively coupled to the can 2374 within the header 2376 by theheader structure holding the wire in proximity to the can 2374.

FIG. 9E shows an implantable medical system 2390 where the shield of alead 2398 is being grounded to a metal can 2394 of an IMD 2392 withinthe header 2396. Proximal electrodes 2402 of the lead 2398 areelectrically connected via wires 2404 to the IMD 2392. Here, acapacitively coupled pathway is being provided between the shield andthe metal can 2394. A coupling 2406 such as a spring loaded connector ora ring electrode contacts the lead 2398 and is in contact with theshield. A shunt plate such as a tab 2408 or similar structure serving asa ground conductor extends from the coupling 2406 toward the can 2394and is capacitively coupled to the can 2394 within the header 2396 bythe header structure holding the tab 2408 in proximity to the can 2394.

FIG. 9F shows an implantable medical system 2410 where the shield of alead 2418 is being grounded to a metal can 2414 of an IMD 2412 withinthe header 2416. Proximal electrodes 2420 of the lead 2418 areelectrically connected via wires 2422 to the IMD 2412. Within the can2414, filter feed through (FFT) circuits 2424 are present tocapacitively couple the wires 2422 to the metal can 2414 while allowingconnection of the wires 2422 to stimulation circuits. The FFT circuits2424 for the electrodes 2420 protects the IMD 2412 from electromagneticbackground noise picked up by the filars, albeit potentially less noisedue to the presence of the shield.

Here, a capacitively coupled pathway is being provided between theshield and the metal can 2414 also via an FFT circuit 2430. A coupling2426 such as a spring loaded connector or a ring electrode contacts thelead 2418 and is in contact with the shield. A wire 2428 serving as aground conductor extends from the coupling 2426 toward the can 2414 andterminates at the FFT circuit 2430 to provide the capacitive couplingbetween the shield and the can 2414.

As shown, the coupling 2426 to the shield may be an existing electrodeof the lead 2418 that provides stimulation signals to a filar within thelead 2418. In that case, the FFT circuit 2430 may provide capacitivecoupling to the can for both the filar and the shield. In such a case,it may be desirable to capacitively couple the shield to the coupling2426 so that relatively low frequency stimulation signals are notpresent on the shield but induced RF current on the shield has a pathwayto the FFT circuit 2430. For example, the outer jacket may separate theshield from the electrode by a separation on the order of 0.5-5 mils toallow an RF coupling to occur. As an alternative to using the samecoupling and FFT circuit for both the shield and the filar, the shieldmay be provided a dedicated coupling 2426 and a dedicated FFT circuit2430 that are independent of any electrodes and filars within the lead2418.

For the examples of FIGS. 9A-9F, various examples of connecting thegrounding conductor to the lead and to the can within the header aredisclosed, using combinations of direct current couplings and capacitivecouplings. It will be appreciated that any combination of these andother examples of direct current coupling and capacitive couplingconnections of the ground conductor may be used to provide thecapacitively coupled pathway that ultimately provides an RF ground fromthe shield within the header to the metal can. For instance, acapacitive coupling may be provided in any of the various embodiments atthe coupling to the shield as discussed above in relation to FIG. 9F.

FIG. 10A shows an implantable medical system 2440 where the shield of alead 2448 is being grounded to a metal can 2444 of an IMD 2442 outsideof the header 2446. Here, a ground pathway is being provided between theshield and a ground plate 2454 installed on the header 2446. The groundplate provides a relatively large surface area in comparison to anindividual electrode and allows for safe dissipation of induced RFcurrent on the shield in the same manner as grounding to the can 2444. Acoupling 2450 such as a spring loaded connector or a ring electrodecontacts the lead 2448 and is in contact with the shield. A wire 2452that serves as a ground conductor is attached to the coupling 2450 by aweld or other bond and extends from the coupling 2450 to the groundplate 2454 where a weld or other bond holds the wire 2452 to the groundplate 2454.

FIG. 10B shows an implantable medical system 2460 where the shield of alead 2468 is being grounded to a metal can 2464 of an IMD 2462 withinthe header 2466. Here, a ground pathway is also being provided betweenthe shield and a ground plate 2474 installed on the header 2466. Acoupling 2470 such as a spring loaded connector or a ring electrodecontacts the lead 2468 and is in contact with the shield. A wire 2472that serves as a ground conductor is attached to the coupling 2470 by aweld or other bond and extends from the coupling 2470 to the groundplate 2474 where a weld or other bond holds the wire 2472 to the groundplate 2474.

FIG. 10C shows an implantable medical system 2480 where the shield of alead 2488 is being grounded to a metal can 2484 of an IMD 2482 withinthe header 2486. Here, a ground pathway is being provided between theshield and a connector block 2492 with a relatively large surface areathat also acts as a ground plate installed on the header 2486. In thisexample, the connector block 2492 is a set screw block that uses a setscrew 2494 to tighten against a coupling 2490 on the lead 2488. Thecoupling 2490 such as a ring electrode contacts the lead 2448 and is incontact with the shield. A set screw 2494 extends from the coupling 2490and through the connector block 2492 and acts as a ground conductor toprovide the ground pathway from the shield to the connector block 2492.Other conductive features may also be present within the connector block2492 to contact the coupling 2490 and provide the RF ground pathway.

For the examples of FIGS. 10A-10C, various examples of connecting thegrounding conductor to the lead and to the ground plate are disclosed.It will be appreciated that any combination of direct current couplingand capacitive coupling connections may be used to provide the pathwaythat ultimately provides an RF ground from the shield to the groundplate. For instance, a capacitive coupling may be provided in any of thevarious embodiments at the coupling to the shield as shown in FIGS.10A-10C and as discussed above in relation to FIG. 9F. Likewise, acapacitive coupling may be present between a ground conductor extendingfrom the coupling to the shield and the ground plate.

Embodiments disclosed in relation to FIGS. 11-15E also provide for radiofrequency (RF) grounding of a shield present within an implantable lead.The shield may be grounded in various ways such as directly to tissue atone or more points along the lead body. The pathway for grounding may bea direct current pathway or be capacitively coupled. The pathway forgrounding may utilize an exposed or nearly exposed shield at one or morepoints along the lead body, metal conductors attached to the lead at oneor more points, a jacket with a conductive doping at one more points,and so forth.

FIG. 11 shows an example of an implantable medical system 3100 thatincludes an IMD 3102 coupled to a lead 3108. The IMD 3102 includes ametal can 3104, typically constructed of a medical grade titanium, suchas grades 1-4, 5 or 9 titanium, or similar other biocompatiblematerials. The IMD 3102 includes a header 3106 typically constructed ofmaterials such as polysulfone or polyurethane, that is affixed to themetal can 3104. The header 3106 is shown transparently for purposes ofillustration. The header 3106 provides a structure for securing the lead3108 to the IMD 3102 and for establishing electrical connectivitybetween circuitry of the IMD 3102 and electrodes of the lead 3108.

The lead 3108 includes electrodes 3116 on a distal end that arepositioned at a stimulation site within a patient. The lead alsoincludes connector rings 3110 on a proximal end that is positionedwithin the header 3106. The connector rings 3110 make physical contactwith electrical connections 3111 within the header. The electricalconnections 3111 may include a metal contact that the connector ring3110 rests against upon being inserted into the header 3106 where a wireextends from the metal contact into the can 3104 where the circuitry ishoused. Signals applied by the IMD 3102 to the connector rings 3110 areconducted through the lead 3108 to the electrodes 3116 to provide thestimulation therapy to the patient.

The lead 3108 is secured in the header 3106 such as by a set screw block3112 within the header 3106 that allows at least one set screw 3114 tobe tightened against at least one of the electrodes 3110. With the lead3108 in place, the shield 3118 of the lead 3108 may then become groundedto the body along one or more points down the length of the lead fromthe IMD 3102.

FIGS. 12A and 12B show an example of the lead 3108, where a shield 3118is present. An outer jacket layer 3120 is shown transparently in FIG.12A for purposes of illustrating the shield 3118. The shield 3118 blocksat least some RF energy from directly coupling to conductive filars 3124that are present within the lead 3108. The conductive filars 3124 extendthe length of the lead and interconnect the proximal electrodes 3110 tothe distal electrodes 3116 so that stimulation signals are conductedfrom the proximal end to the distal end of the lead 3108.

As shown in FIG. 12A, the shield 3118 of this example is a braided metalwire. The metal wire may be constructed of various materials such astitanium, tantalum, niobium, platinum-iridium alloy, platinum,palladium, gold, stainless steel, and their alloys, or other metals. Itmay be desired to utilize a biocompatible metal for the shield 3118,particularly for embodiments where a portion of the shield 3118 may beexposed for purposes of grounding. While the shield 3118 is shown as abraid, other shield configurations may be chosen particularly whereflexibility is not an issue such as a foil strip wrapped about the lead3108 in an overlapping manner or an outer layer 3120 that is heavilydoped with conductive particles.

As shown in FIG. 12B, the shield 3118 may be embedded within the jacketof the lead 3108. One manner of constructing the lead 3108 with theshield 3118 is to provide an inner jacket 3122 that encloses the filars3124 and any additional insulation layer 3126, such aspolytetrafluoroethylene (PTFE) that may surround each filar 3124. Theshield 3118 may then reside on the outer portion of the inner jacket3122, and the outer jacket 3120 may then enclose the shield 3118. Theouter jacket 3120 maybe added over the braid 3118, or it may be extrudedover the braid.

For embodiments where it is desirable for the shield 3118 to RF coupleto tissue, typically as capacitive coupling, either as an alternative togrounding at the can of the IMD or in addition to grounding at the can,the amount of the outer jacket layer 3120 covering the shield 3118 maybe relatively thin, such as on the order of 0.5 to 5 mils. Where theshield 3118 grounds at one or more specific locations along its length,via a direct current coupling or a capacitive coupling, the shield maybe located further from the outer surface of the lead 3108 withadditional features of the lead providing the coupling at the one ormore specific locations as discussed below.

The inner and outer jackets 3122, 3120 may be constructed of the same orsimilar materials such as various flexible and biocompatible polymers,examples of which are polyurethanes, and silicones. A lumen 3128 may beincluded inside of the inner jacket 3122 around which the insulatedfilars 3124 are coiled or otherwise positioned. The lumen 3128 may beuseful, particularly for percutaneous leads 3108, to allow a stylet tobe inserted for purposes of pushing and steering the lead 3108 into thedesired position within the patient.

FIG. 12C shows one example of exposing the shield 3118 at a particularpoint along the lead 3108 for purposes of grounding the shield 3118. Inthis example, the outer layer 3120 of the jacket has been removed at afirst point along the lead 3108 distant from the distal end to exposethe shield 3118 and the inner jacket 3122. For example, an excimer lasermay be used to ablate the outer layer 3120. Physical contact may then beestablished between the shield 3118 and the tissue or between the shield3118 and an electrode attached to the lead.

FIG. 12D shows another example of providing a pathway to ground theshield 3118. Here, a metal conductor, specifically a ring electrode3130, is attached at the first point along the lead 3108 distant fromthe distal end to provide a robust physical connection to the tissuewhile avoiding tissue in-growth that may occur if the shield 3118 isexposed directly. Depending upon the embodiment, a coupling of theshield 3118 to the electrode 3130 may be a direct current coupling or acapacitive coupling, either providing a pathway for RF current to passto ground. The ring electrode 3130 may be attached by methods such ascrimping, clamping, welding, and the like.

FIG. 12E shows an example of nearly exposing the shield 3118 at aparticular point along the lead 3108 for purposes of grounding theshield 3118. In this example, the outer layer 3120 of the jacket hasbeen almost entirely removed at a first point along the lead 3108distant from the distal end to nearly expose the shield 3118 and theinner jacket 3122. Only a very thin layer 3120′, on the order of about0.5-5 mils, of the outer layer 3120 is remaining. Physical contactbetween the shield 3118 and the tissue is avoided so that tissuein-growth does not occur, and the shield 3118 capacitively couples tothe tissue to provide the RF pathway to ground.

FIG. 12F shows an example of exposing, or nearly exposing, the shield3118 at a plurality of points 3202 along the lead. At these points 3202,the outer layer 3120 has been at least partially ablated or otherwiseremoved to place the shield 3118 in closer proximity to the body tissueso that an RF pathway to ground is established. Where the shield 3118 isexposed, the RF pathway is a direct current coupling to the tissue.Where the shield 3118 is nearly exposed, the RF pathway is a capacitivecoupling to the tissue.

Where multiple points of the RF pathway to ground are present, aparticular separation of the multiple points is provided. A nearestedge-to-nearest edge distance between one point and an adjacent one isshown by the distance from edge 3204 to edge 3206. Where the outer layeris removed, the flexibility and strength of the lead is altered for theregion including those points and this distance from edge 3204 to edge3206 can be used to control the flexibility and strength.

Where multiple points of the RF pathway to ground are direct currentcouplings, another concern is current induced by the gradient magneticfields present in a magnetic resonance (MR) scan. If the most proximaland most distal points of the direct current coupling are spaced too farapart, then the magnetic gradient may induce a dangerous current throughthe shield and produce a significant stimulation of tissue at thoseground points along the lead. Therefore, choosing the nearestedge-to-nearest edge separation to fall within an illustrative range of2 millimeters (mm) or more with a most proximal to most distalseparation, such as edge 3204 to edge 3208, of about 40 centimeters (cm)or less may allow for flexibility of the lead in the region whilemaintaining small loops that prevent large magnetic gradient inducedcurrents should the shield be exposed at the points 3202.

FIG. 12G shows an example of coupling the shield 3118 to ground with aplurality of metal conductors such as rings 3130 at a plurality ofpoints 3210 along the lead. At these points 3202, the outer layer 3120has been at least partially ablated or otherwise removed to place theshield 3118 in close proximity with the metal conductors 3130 so that anRF pathway to ground is established through the metal conductors 3130.Where the shield 3118 is exposed to the metal conductors 3130, the RFpathway is a direct current coupling to the tissue. Where the shield3118 is nearly exposed to the metal conductors 3130, the RF pathway is acapacitive coupling to the tissue.

As with the example of FIG. 12F, where multiple points of the RF pathwayto ground are present, a particular separation of the multiple points isprovided. A nearest edge-to-nearest edge distance between one point andan adjacent one is shown by the distance from edge 3212 to edge 3214.The flexibility and strength of the lead is altered for the regionincluding those points, with the metal conductors 3130 limiting thebending in this region to essentially those sections of lead between themetal conductors 3130. Thus, in one example, a nearest edge-to-nearestedge distance may be maintained at or above 2 mm or 50% of the groundingring length so that flexibility of the lead is maintained.

Also, where the shield 3118 is direct current coupled to the metalconductors 3130, a magnetic gradient induced current is of concernbecause the metal conductors 3130 have a direct current coupling to thetissue. In that case, the separation of the most proximal to the mostdistal may be kept within a range that prevents a large loop and avoidsa large magnetic induced gradient current. In this particular example,the most proximal to the most distal distance, such as from edge 3212 toedge 3216, may be maintained at or below approximately 40 cm so thatmagnetic gradient induced currents are insignificant.

FIG. 12H shows a cross-section of the lead 3108 at a particular pointwhere the outer jacket 3120 has been ablated or otherwise removed. Inthis example, the lead 3108 at this particular point includes a metalconductor 3130 with a direct current coupling to the shield 3118. Theouter layer 3120 of the jacket has been removed to allow the metalconductor 3130, a ground ring as shown, to wrap around the lead andcontact the shield 3118. The filars may be present within the innerjacket 3122 or any other inner layer as shown or within the lumencreated by the inside wall of the inner jacket 3122 or any other innerlayer as shown in FIG. 12B.

FIG. 12I shows a cross-section of the lead 3108 at a particular pointwhere the outer jacket 3120 has been ablated or otherwise removed. Inthis example, the lead 3108 at this particular point has the shield 3118exposed to tissue for a direct current coupling by entirely removing theouter layer 3120. The filars may be present within the inner jacket 3122or any other inner layer as shown or within the lumen created by theinside wall of the inner jacket 3122 or any other inner layer as shownin FIG. 12B.

FIG. 12J shows a cross-section of the lead 3108 at a particular pointwhere a portion of the outer jacket 3120 has been ablated or otherwiseremoved. In this example, the lead 3108 at this particular pointincludes a metal conductor 3130 with a capacitive coupling to the shield3118. The outer layer 3120 of the jacket has been partially removed,with a remaining thickness of about 0.5 mils to 5 mils, to nearly exposethe shield 3118. This allows the metal conductor 3130, a ground ring asshown, to wrap around the lead and capacitively couple with the shield3118 at RF frequencies. The filars may be present within the innerjacket 3122 or any other inner layer as shown or within the lumencreated by the inside wall of the inner jacket 3122 or any other innerlayer as shown in FIG. 12B.

FIG. 12K shows a cross-section of the lead 3108 at a particular pointwhere a portion of the outer jacket 3120 has been ablated or otherwiseremoved. The outer layer 3120 of the jacket has been partially removed,with a remaining thickness of about 0.5 mils to 5 mils, to nearly exposethe shield 3118. The shield 3118 capacitively couples to the tissue atRF frequencies. The filars may be present within the inner jacket 3122or any other inner layer as shown or within the lumen created by theinside wall of the inner jacket 3122 or any other inner layer as shownin FIG. 12B.

FIG. 13A shows an example of a ring electrode 3220 that may be attachedto a lead 3108 to form the RF pathway to ground from the shield 3118.The ring electrode may be constructed of platinum, platinum-iridium,titanium, tantalum, stainless steel, and other similar biocompatiblemetals. The ring electrode 3220 may have a gap 3222. The ring electrode3220 may be sprung open to fit around the lead at the particular pointwhere the jacket has been ablated, and the ring electrode 3220 iscrimped back into a tightly fitting configuration. As another example,the ring electrode 3220 may be flat and then rolled into the ring shapeabout the lead. In some examples, the gap 3222 may close upon crimpingwhile in other embodiments the gap 3222 may remain to some degree.

FIG. 13B shows an example of another ring electrode 3224 that may beattached to a lead 3108 to form the RF pathway to ground from the shield3118. The ring electrode 3224 includes a tab 3226 that extends away fromthe lead to provide an additional surface area and extension into thetissue for adding grounding of the shield 3118. The ring electrode 3220may be sprung open to fit around the lead at the particular point wherethe jacket has been ablated and the ring electrode 3220 is crimped backinto a tightly fitting configuration. As in the previous example, thering electrode 3224 may be flat and then rolled into the ring shapeabout the lead while maintaining a flat portion as the tab 3226.

FIG. 13C shows an example of another ring electrode 3228 that may beattached to a lead 3108 to form the RF pathway to ground from the shield3118. The ring electrode 3228 forms a helix. The ring electrode 3228 maybe sprung open to fit around the lead at the particular point where thejacket has been ablated and the ring electrode 3228 is crimped back intoa tightly fitting helical configuration. As in the previous examples,the ring electrode 3228 may be flat and then rolled into the helicalring shape about the lead.

FIG. 13D shows an example of a ring electrode 3230 that may be attachedto a lead 3108 to form the RF pathway to ground from the shield 3118.The ring electrode 3230 has an outer side 3234 that faces away from theshield 3118 and an inner side 3236 that faces toward the shield 3118 andmay directly contact the shield 3118. In this example, the outer side3234 has a non-conductive coating 3232 applied so that the outer side3234 does not have a direct coupling to the tissue. The non-conductivecoating may be of various types such as polyurethane, silicone or otherbiocompatible polymers.

The inner side 3236 may either have a direct current coupling or acapacitive coupling to the shield. With multiple ring electrodes 3230 inplace on a lead, magnetic gradient induced current which is at arelatively low frequency is not a concern because the non-conductivecoating 3232 prevents the relatively low frequency induced current fromflowing to the tissue. Thus, the distance between adjacent electrodes isnot limited by induced current concerns. Meanwhile, the high frequencyRF induced current does ground to the tissue through the capacitivecoupling provided by the non-conductive coating 3232.

FIG. 13E shows an example of a ring electrode 3240 that may be attachedto a lead 3108 to form the RF pathway to ground from the shield 3118.The ring electrode 3240 has an outer side 3242 that faces away from theshield 3118 and an inner side 3244 that faces toward the shield 3118 andmay directly contact the shield 3118. In this example, the inner side3244 has a non-conductive coating 3246 applied so that the inner side3244 does not have a direct coupling to the shield 3118 even if theshield 3118 is entirely exposed to the ring electrode 3240. Thenon-conductive coating 3246 may be of the various types discussed abovein the previous example.

The outer side 3242 may have a direct current coupling to the tissue.With multiple ring electrodes 3240 in place on a lead, magnetic gradientinduced current is not a concern because the non-conductive coatingprevents the relatively low frequency induced current from flowing fromthe shield 3118 to the ring electrode 3240. Thus, the distance betweenadjacent electrodes is not limited by induced current concerns.Meanwhile, the high frequency RF induced current does ground through thering electrode 3240 to the tissue through the capacitive couplingprovided by the non-conductive coating 3246.

FIG. 13F shows an example of a ring electrode 3250 that may be attachedto a lead 3108 to form the RF pathway to ground from the shield 3118.The ring electrode 3250 has an outer side 3252 that faces away from theshield 3118 and may directly contact the tissue and an inner side 3254that faces toward the shield 3118 and may directly contact the shield3118. In this example, both the inner side 3254 and the outer side 3252have a non-conductive coating 3256 applied. The inner side 3254 does nothave a direct current coupling to the shield 3118 even if the shield isentirely exposed to the ring electrode 3250. The outer side 3252 doesnot have a direct current coupling to the tissue even if in physicalcontact with the tissue. The non-conductive coating 3256 may be of thevarious types discussed above in the previous examples.

With multiple ring electrodes 3250 in place on a lead, magnetic gradientinduced current is not a concern because the non-conductive coatingprevents the relatively low frequency induced current from flowing fromthe shield 3118 to the ring electrode 3250. Thus, the distance betweenadjacent electrodes is not limited by induced current concerns.Meanwhile, the high frequency RF induced current does ground through thering electrode 3250 to the tissue through the capacitive couplings oneach side of the ring electrode 3250 provided by the non-conductivecoating 3256.

While the examples of FIGS. 13A-13F show various shapes of ringelectrodes, it will be appreciated that various other shapes are alsoapplicable for metal conductors being attached to the lead to providethe RF ground pathway. Furthermore, while FIGS. 13D-13F show aparticular ring electrode shape with a non-conductive coating, it willbe appreciated that the non-conductive coating is applicable to eitheror both sides of any of the metal conductor configurations includingthose of FIGS. 13A-13C.

FIG. 14A shows a cross-section of a lead 3260 that includes an outerjacket layer 3266 that surrounds a shield 3262 and an inner jacket layer3264. The outer jacket layer 3266 is doped with conductive particles3268 at a particular point along the length of the lead. Theseconductive particles 3268 provide RF conductive qualities for the outerjacket layer 3266. Thus, the RF energy couples from the shield 3262 tothe tissue through the doped outer jacket layer 3266. Examples of theconductive particles include carbon, tantalum, titanium, platinum,platinum-iridium, and other biocompatible conductive substances. Thefilars may be present within the inner jacket 3264 or any other innerlayer as shown or within the lumen created by the inside wall of theinner jacket 3264 or any other inner layer like that shown in FIG. 12B.

FIG. 14B shows the lead 3260 with a plurality of points 3272 along thelead where the conductive particles 3268 are present within the outerlayer 3266. The doped outer layer 3266 is exposed to create the RFpathway to ground from the outer layer 3266 to the tissue.

FIG. 14C shows a cross-section of a lead 3260 where the outer jacketlayer 3266 that surrounds a shield 3262 has been removed via ablation orother technique to expose the shield 3262 and the inner jacket layer3264. Here, the inner jacket layer 3264 is doped with conductiveparticles 3268 at least at the particular point(s) along the length ofthe lead where the outer layer 3266 has been removed. These conductiveparticles 3268 provide RF conductive qualities for the outer portion ofthe inner jacket layer 3264 where the shield 3262 is present. Thus, theRF energy couples from the shield 3262 to the tissue through the dopedjacket layer 3264. The filars may be present within the inner jacket3264 or any other inner layer as shown or within the lumen created bythe inside wall of the inner jacket 3264 or any other inner layer likethat shown in FIG. 12B.

FIG. 14D shows the lead 3260 with a plurality of points 3274 along thelead where the conductive particles 3268 are present within the innerlayer 3264. The outer layer 3266 is removed at these points 3274 toexpose the doped inner layer 3264 and to create the RE pathway to groundfrom the inner layer 3264 to the tissue.

FIGS. 15A and 15B show an example of an implantable medical lead 3108where a lead anchor 3280 is attached. In this example, the lead anchor3280 is an RF conductor to the tissue to provide the ground pathway forthe shield 3118. In this particular example, the lead 3108 includes aring electrode 3130 that is coupled to the shield 3118, either via adirect current coupling or a capacitive coupling. The lead anchor 3280is constructed of metal or other conductor, or at least has a portionthat is or conductive and directly contacts or nearly contacts the ringelectrode 3130 and the tissue to ground the shield 3118 at RFfrequencies. This ground pathway is secured in place via theconventional mounting of the lead anchor 3280 to the lead body and bythe wings 3282 being sutured in place to the tissue. The filars may bepresent within the inner jacket or any other inner layer as shown orwithin the lumen created by the inside wall of the inner jacket or anyother inner layer like that shown in FIG. 12B.

FIGS. 15C and 15D show another example of an implantable medical lead3108 where a lead anchor 3280 is attached. In this example, the leadanchor 3280 is an RF conductor to the tissue to provide the groundpathway for the shield 3118. In this particular example, the lead 3108does not have a ring electrode 3130 coupled to the shield 3118. However,as seen in FIG. 15D, the lead anchor has gripping teeth 3284 that sinkinto the outer layer of the jacket and either directly contact or nearlycontact the shield 3118. The filars may be present within the innerjacket or any other inner layer as shown or within the lumen created bythe inside wall of the inner jacket or any other inner layer like thatshown in FIG. 12B.

Directly contacting the shield 3118 creates a direct current coupled RFpathway while nearly contacting the shield 3118 creates a capacitivelycoupled RF pathway. As with the previous example, the lead anchor 3280is constructed of metal or other conductor, or at least has a portionthat is conductive and contacts or nearly contacts the tissue to groundthe shield 3118 at RF frequencies. This ground pathway is secured inplace via the conventional mounting of the lead anchor to the lead bodyand by the wings 3282 being sutured in place to the tissue.

In these embodiments, the anchor may capacitively couple to the shield3118 without teeth or rings being present, particularly where the depthof the shield within the outer layer 3120 is relatively small. Forexample, for depth of the shield 3118 of about 5 mils or less, theanchor may reside on the outer layer 3120 and capacitively couple to theshield 3118 to provide the RF pathway to ground.

FIG. 15E shows an example of an implantable medical lead 3108 where alead anchor 3290 is attached. In this example, the lead anchor 3290 isan RF conductor to the tissue to provide the ground pathway for theshield 3118. However, in this particular example, lead anchor 3290provides a capacitive coupling to ground by utilizing a non-conductiveouter material or coating 3292 to contact the tissue. The lead anchor3290 may have either a direct current coupling or capacitive coupling tothe shield 3118, or ring electrode 3130 if any. The capacitive couplingto the tissue prevents the lead anchor 3290 from becoming a magneticgradient induced current electrode, such as where other shieldelectrodes are present at other points along the lead 3108.

Utilizing an anchor to provide an RF pathway to ground, as shown inFIGS. 15A-15E, may also be useful considering that the typical mountinglocation of an anchor is at a point where the intensities of the RFfields change. For instance, an anchor may be positioned near the entryhole of the cranium where the lead 3108 is used for brain stimulation.The intensities of the field may change from one side of the entry holeto the other and providing the RF pathway to ground via an anchor nearthe entry hole may assist in dissipating energy received by the shield3118 externally of the entry hole to prevent such energy from travelingthrough the shield 3118 and through the entry hole toward the shieldtermination which is closer to the stimulation electrodes.

Embodiments disclosed in relation to FIGS. 16-17G provide for shieldingof both an implantable medical lead and an implantable lead extension.The two shields are interconnected with a radio frequency (RF)conductive path to maintain a continuity of the shielding along thelength between the implantable medical device (IMD) and the stimulationsite.

FIG. 16 shows an example of an implantable medical system 4100 thatincludes an IMD 4102 coupled to a lead 4108. The IMD 4102 includes ametal can 4104, typically constructed of a medical grade titanium, suchas grades 1-4, 5 or 9 titanium, or similar other biocompatiblematerials. The IMD 4102 includes a header 4106 typically constructed ofmaterials such as polysulfone or polyurethane, that is affixed to themetal can 4104. The header 4106 is shown transparently for purposes ofillustration. The header 4106 provides a structure for securing the leadextension 4142 to the IMD 4102 and for establishing electricalconnectivity between circuitry of the IMD 4102 and distal connectors ofthe lead extension 4142 that are located in a distal housing 4140.

The extension 4142 also includes ring connectors 4110 on a proximal endthat is positioned within the header 4106. The ring connectors 4110 makephysical contact with electrical connections within the header. Theelectrical connections may include a metal contact that the ringconnector 4110 rests against upon being inserted into the header 4106where a wire extends from the metal contact into the can 4104 where thecircuitry is housed. Signals applied by the IMD 4102 to the ringconnectors 4110 are conducted through the extension 4142 to theconnectors within the housing 4140 to provide the stimulation signals tothe lead 4108. The extension 4142 is secured in the header 4106 such asby a set screw block 4112 within the header 4106 that allows at leastone set screw 4114 to be tightened against at least one of the ringconnectors 4110.

The lead 4108 includes electrodes 4116 on a distal end that arepositioned at a stimulation site within a patient. The lead 4108 alsoincludes ring connectors on a proximal end that is positioned within thehousing 4140. The ring connectors make physical contact with electricalconnections within the housing 4140. The electrical connections mayinclude a metal contact such as a Bal Seal® connector of the Bal SealEngineering, Inc. of Foothill Ranch, Calif., another spring loadedconnector, or a set screw block that the electrode rests against uponbeing inserted into the housing 4140. A wire extends from the metalcontact of the housing 4140 into the extension 4142 to connect with thefilars of the extension 4142. Signals applied by the IMD 4102 to thering connectors 4110 are conducted through the extension 4142 and lead4108 to the electrodes 4116 to provide the stimulation therapy to thepatient.

The lead 4108 is secured in the housing 4140 such as by a set screwblock within the housing 4140 that allows at least one set screw to betightened against at least one of the electrodes. A shield 4144 of theextension and a shield 4118 of the lead 4108 that are discussed belowwith reference to FIGS. 17A-17G are present to prevent the induced RFcurrent on the filars. The shields 4118, 4144 may be grounded at the IMD4102 of FIG. 16 or at various grounding points established along theextension 4142 and/or lead 4108. As another option, the shield 4144 ofthe extension 4142 and/or the shield 4118 of the lead 4108 may belocated within the extension 4142 or lead 4108 at a small distance fromthe surface so that the shields 4118, 4144 will effectively capacitivelycouple to the tissue along the length of the lead to dissipate energy tothe tissue over the length. In any of these cases, continuity may bemaintained between the shields 4118 and 4144 as discussed herein

FIGS. 17A-17G show examples of the extension 4142 and lead 4108 whereshields 4118, 4144 are present. The lead 4108 is inserted through anopening 4146 in the housing 4140 on the distal end of the extension4142. Outer jacket layers 4120, 4141 for the lead 4108 and extension4142 are shown transparently in FIG. 17A for purposes of illustratingthe shields 4118, 4144. The shields 4118, 4144 block at least some RFenergy from directly coupling to conductive filars that are presentwithin the lead 4108 and extension 4142. The conductive filars extendthe length of the extension 4142 and lead 4108 and interconnect theproximal connector rings 4110 of the extension 4142 to the distalelectrodes 4116 of the lead 4108 so that stimulation signals areconducted to the stimulation site.

As shown in FIG. 17A, the shields 4118, 4144 of this example are braidedmetal wires. The metal wire may be constructed of various materials suchas titanium, tantalum, niobium, platinum-iridium alloy, platinum,palladium, gold, stainless steel, and their alloys, or other metals. Itmay be desirable to utilize a biocompatible metal for the shields 4118,4144, particularly for embodiments where a portion of the shields 4118,4144 may be exposed for purposes of grounding. While the shield 4118 isshown as a braid, other shield configurations may be chosen particularlywhere flexibility is not an issue such as a foil strip wrapped about thelead 4108 in an overlapping manner or an outer layer 4120 that isheavily doped with conductive particles.

FIG. 17A also shows a set screw block 4143 present on the housing 4140.The set screw block 4143 may be used to fix the proximal end of the lead4108 in place within the opening 4146 of the housing 4140 where a setscrew is tightened against a connector ring on the lead 4108. Othermanners of fixing the lead 4108 within housing 4140 may also be used.

FIG. 17B shows a coupling of the lead 4108 to the housing 4140 as across-section taken through the coupling of a shield connector 4132 to ashield electrode 4130. The shield 4118 of the lead 4108 may be embeddedwithin the jacket of the lead 4108. One manner of constructing the lead4108 with the shield 4118 is to provide an inner jacket 4122 thatencloses the filars 4124 and any additional insulation layer 4126, suchas polytetrafluoroethylene (PTFE) that may surround each filar 4124. Theshield 4118 may then reside on the outer portion of the inner jacket4122, and the outer jacket 4120 may then enclose the shield 4118. Theouter jacket 4120 maybe added over the braid 4118, or it may be extrudedover the braid.

For embodiments where it is desirable for the shield 4118 to RF coupleto tissue, typically as a capacitive coupling, either as an alternativeto or in addition to grounding at the can of the IMD or elsewhere, theamount of the outer jacket layer 4120 covering the shield 4118 may berelatively thin, such as on the order of 0.5 to 5 mils. Where the shield4118 grounds at the can of the IMD and grounding via a capacitivecoupling from the shield through the outer jacket 4120 directly to thetissue is of less significance, then the shield 4118 may be locatedfurther from the outer surface of the lead 4108.

The inner and outer jackets 4122, 4120 may be constructed of the same orsimilar materials such as various flexible and biocompatible polymers,examples of which are polyurethanes, and silicones. A lumen 4128 may beincluded inside of the inner jacket 4122 around which the insulatedfilars 4124 are coiled or otherwise positioned. The lumen 4128 may beuseful, particularly for percutaneous leads 4108, to allow a stylet tobe inserted for purposes of pushing and steering the lead 4108 into thedesired position within the patient.

To provide a robust connection for the shield 4118, the shield electrode4130 such as an electrode ring may be wrapped around the outer layer4120 to contact the shield 4118 and provide a direct current coupling tothe shield 4118. A direct current coupling between the shields avoidslarge variations in the characteristic impedance for the shielding fromthe extension 4142 to the lead 4108. Avoiding variations in thecharacteristic impedances may reduce the degree of RF reflection thatoccurs within the shield 4118, which in turn reduces the amount of RFheating that may occur via the stimulation electrodes.

The housing 4140 includes the shield connector 4132, such as a set screwblock, a Bal Seal® connector, or another spring loaded connector. Theshield connector 4132 of this embodiment is enclosed within a housinglayer 4134 and contacts the shield electrode 4130 of the lead 4108. Thehousing layer 4134 may be constructed of various non-conductivematerials such as polyurethane, polysulfone, nylon, silicone andpolyetheretherketone (PEEK) and provides a relatively rigid structuresimilar to that provided by the header 4106 of the IMD 4102.

A shield jumper wire 4136 is included in this embodiment within thehousing layer 4134. The shield jumper wire 4136 contacts the shieldconnector 4132 and extends from the shield connector 4132 into thehousing layer 4134 and extends proximally to the shield 4144 within theextension 4142. The shield jumper wire 4136 may be welded, crimped, orotherwise affixed to the shield conductor 4132 and the shield 4144.

FIG. 17C shows an example similar to the example of FIG. 17B. The lead4108 is constructed in the same manner. However, the housing 4140utilizes a different construction. In the housing 4140, a housing shield4138 is present and extends to the shield conductor 4132 where thehousing shield 4138 contacts the shield connector 4132. No juniper wireis needed because the housing shield 4138 establishes continuity of theshielding from the shield connector 4132 to the shield 4144 presentwithin the extension 4142.

The housing shield 4138 may be affixed to the shield connector 4132 invarious ways. For instance, the housing shield 4138 may be welded orcrimped to the shield connector 4132 to provide a direct currentcoupling. In some embodiments, the shield connector 4132 is distalrelative to stimulation connectors of the housing 4140. In those cases,extending the housing shield 4138 through the housing 4140 to the shieldconnector 4132 provides additional shielding protection from RF inducedcurrents.

FIG. 17D shows the lead 4108 coupled to the housing 4140 with across-section through a stimulation electrode coupling for embodimentsof the housing 4140 that include a shield jumper wire 4136. The lead4108 includes a stimulation connector 4150 and a stimulation jumper wire4156 that interconnects the filar 4124 to the stimulation connector4150. The housing 4140 includes a stimulation connector 4152 thatcontacts the stimulation connector 4150 to form a direct currentcoupling. A stimulation jumper wire 4154 of the housing 4140 contactsthe stimulation connector 4152 and extends through the housing layer4134 in the proximal direction to a corresponding filar within theextension 4142.

As shown in FIG. 17D, both the shield jumper wire 4136 and thestimulation jumper wire 4154 are present within the housing layer 4134.Separation between them is provided to avoid transferring significant RFenergy being captured by the shields 4118, 4144 from the shield jumperwire 4136 to the stimulation jumper wire 4154. For instance, theseparation may be in the range of 0.1 millimeters (mm) to 2.0 mm wherethe housing layer 4134 is constructed of polyurethane, polysulfone,nylon, and PEEK or has a dielectric property of between about 2 and 10.

FIG. 17E shows the lead 4108 coupled to the housing 4140 with across-section through a stimulation connector coupling for embodimentsof the housing 4140 that include the housing shield 4138 extendingthrough the housing 4140. The lead 4108 includes the stimulationconnector 4150 and the stimulation jumper wire 4156 that interconnectsthe filar 4124 to the stimulation connector 4150. The housing 4140includes the stimulation connector 4152 that contacts the stimulationconnector 4150 to form a direct current coupling. The stimulation jumperwire 4154 of the housing 4140 contacts the stimulation connector 4152and extends in the proximal direction to a corresponding filar withinthe extension 4142.

As shown in FIG. 17E, the housing shield 4138 and the stimulation jumperwire 4154 are present within different layers of housing material. Thestimulation jumper wire 4154 is present within a housing inner layer4162 while the housing shield 4138 is present about the housing innerlayer 4162. A housing outer layer 4160 surrounds the housing shield 4138and the housing inner layer 4162. The housing inner layer 4162 and thehousing outer layer 4160 may be constructed of various non-conductivematerials such as those discussed above for the housing layers 4134, andthese layers 4160, 4162 may be the same or different non-conductivematerials. Separation like that discussed above between the stimulationjumper wire 4154 and the housing shield 4138 is provided to avoidtransferring significant RF energy being captured by the shields 4118,4144 from the housing shield 4138 to the stimulation jumper wire 4154.

FIG. 17F shows an embodiment of the housing 4140 where the shield jumperwire 4136 is present. The shield jumper wire 4136 has an attachmentpoint 4172 such as a weld or crimp to the shield connector 4132 wherethe shield electrode 4130 is seated. The shield jumper wire 4136 hasanother attachment point 4184 such as a weld or crimp to the shield 4144of the extension 4142.

The stimulation jumper wires 4154, 4182 have attachment points 4174,4178 such as a weld or crimp to the stimulation connectors 4152 wherethe stimulation electrodes 4150, 4176 are seated. Only two stimulationjumper wires 4154, 4182 are shown for purposes of clarity, and it willbe appreciated that any number of stimulation connectors andcorresponding stimulation jumper wires may be present within the housing4140. As shown, separation is provided between the shield jumper wire4136 and the stimulation jumper wires 4154, 4182 to avoid transferringRF energy to the stimulation jumper wires 4154, 4182.

FIG. 17G shows an embodiment of the housing 4140 where the housingshield 4138 is present. The housing shield 4138 has attachment points4186 such as welds or crimps to the shield connector 4132 where theshield electrode 4130 is seated. The housing shield 4138 continuesthrough the housing out layer 4160 while surrounding the housing innerlayer 4162. The housing shield 4138 transitions to the extension shield4144 upon reaching the junction of the housing 4140 to the body of theextension 4142. In other embodiments, the housing shield 4138 may beattached to the shield 4144 via welds or crimps rather thantransitioning into the body of the extension 4142 as the shield 4144.

The stimulation jumper wires 4154, 4182 have attachment points 4174,4178 to the stimulation connectors 4152 where the stimulation electrodes4150, 4176 are seated. As shown, separation is provided between thehousing shield 4138 and the stimulation jumper wires 4154, 4182 to avoidtransferring RF energy to the stimulation jumper wires 4154, 4182.

Embodiments as disclosed in relation to FIGS. 18-29 provide fortermination of a radio frequency (RF) shield present within animplantable medical lead for use with an implantable medical device(IMD). The shield may be terminated in various ways such as byterminating at an edge of a butt, scarf, or lap joint to an insulationextension. Furthermore, the shield termination may include features suchas a ring attached at the shield termination point within theinsulation, shield wires with folded over ends, or barbs between theinsulation layers.

FIG. 18 shows an example of an implantable medical system 5100 thatincludes an IMD 5102 coupled to a lead 5108. The IMD 5102 includes ametal can 5104, typically constructed of a medical grade titanium, suchas grades 1-4, 5 or 9 titanium, or similar other biocompatiblematerials. The IMD 5102 includes a header 5106 typically constructed ofmaterials such as polysulfone or polyurethane, that is affixed to themetal can 5104. The header 5106 is shown transparently for purposes ofillustration. The header 5106 provides a structure for securing the lead5108 to the IMD 5102 and for establishing electrical connectivitybetween circuitry of the IMD 5102 and electrodes of the lead 5108.

The lead 5108 includes electrodes 5116 on a distal end that arepositioned at a stimulation site within a patient. The lead alsoincludes connector rings 5110 on a proximal end that is positionedwithin the header 5106. The connector rings 5110 make physical contactwith electrical connections 5111 within the header. The electricalconnections 5111 may include a metal contact that the connector ring5110 rests against upon being inserted into the header 5106 where a wireextends from the metal contact into the can 5104 where the circuitry ishoused. Signals applied by the IMD 5102 to the connector rings 5110 areconducted through the lead 5108 to the electrodes 5116 to provide thestimulation therapy to the patient.

The lead 5108 is secured in the header 5106 such as by a set screw block5112 within the header 5106 that allows at least one set screw 5114 tobe tightened against at least one of the connector rings 5110. A shield5118 as shown in FIGS. 19A and 19B may be grounded to the body along oneor more points down the length of the lead from the IMD 5102 via groundrings and/or the shield 5118 may be grounded at the can 5104 of the IMD5102 of FIG. 18. As another option, the shield 5118 may be locatedwithin the lead 5108 at a small distance from the surface so that theshield 5118 will effectively capacitively couple to the tissue along thelength of the lead to dissipate energy to the tissue over the length.

Regardless of the manner of grounding, the shield 5118 terminates on oneend near the proximal end and on the opposite end near the distal end ofthe lead 5108. At the termination point, shields having multiple metalwires such as braided shields are subject to fraying and shield wiremigration. Preventing the shield wire from fraying and/or migrating tothe tissue or to stimulation conductors within the lead 5108 may bedesirable to prevent RF energy captured by the shield 5118 from beingdirected onto a small area of tissue via an electrode or exposed shieldwire.

FIGS. 19A and 19B show an example of the lead 5108, where a shield 5118is present. An outer insulation layer 5120 of a lead jacket is showntransparently in FIG. 19A for purposes of illustrating the shield 5118.The shield 5118 blocks at least some RF energy from directly coupling toconductive filars 5124 that are present within the lead 5108. Theconductive filars 5124 extend the length of the lead and interconnectthe proximal electrodes 5110 to the distal electrodes 5116 so thatstimulation signals are conducted from the proximal end to the distalend of the lead 5108.

As shown in FIG. 19A, the shield 5118 of this example is a braidedcollection of metal wires. The metal wires may be constructed of variousmaterials such as titanium, tantalum, niobium, platinum-iridium alloy,platinum, palladium, gold, stainless steel, and their alloys, or othermetals. It may be desired to utilize a biocompatible metal for theshield 5118, particularly for embodiments where a portion of the shield5118 may be exposed for purposes of grounding. While the shield 5118 isshown as a braid, other shield configurations may be chosen particularlywhere flexibility is not an issue such as a foil strip wrapped about thelead 5108 in an overlapping manner or an outer layer 5120 that isheavily doped with conductive particles.

As shown in FIG. 19B, the shield 5118 may be embedded within the jacketof the lead 5108. One manner of constructing the lead 5108 with theshield 5118 is to provide an inner insulation layer 5122 of the jacketthat encloses the filars 5124 and any additional insulation layer 5126,such as polytetrafluoroethylene (PTFE) that may surround each filar5124. The shield 5118 may then reside on the outer portion of the innerinsulation layer 5122, and the outer insulation layer 5120 may thenenclose the shield 5118. The outer jacket 5120 maybe added over thebraid 5118, or it may be extruded over the braid.

For embodiments where it is desirable for the shield 5118 to RF coupleto tissue, typically as a capacitive coupling, either as an alternativeto grounding at the can 5104 of the IMD 5102 or at specific points alongthe lead 5108 or in addition to such grounds, the amount of the outerjacket layer 5120 covering the shield 5118 may be relatively thin, suchas on the order of 0.5 to 5 mils. Where the shield 5118 grounds at oneor more specific locations along its length, via a direct currentcoupling or a capacitive coupling, the shield 5118 may be locatedfurther from the outer surface of the lead 5108 with additional featuresof the lead providing the coupling at the one or more specific locationsas discussed below.

The inner and outer insulation layers 5122, 5120 of the jacket may beconstructed of the same or similar materials such as various flexibleand biocompatible polymers, examples of which are polyurethane, andsilicones. A lumen 5128 may be included inside of the inner jacket 5122around which the insulated filars 5124 are coiled or otherwisepositioned. The lumen 5128 may be useful, particularly for percutaneousleads 5108, to allow a stylet to be inserted for purposes of pushing andsteering the lead 5108 into the desired position within the patient.

FIG. 20 shows an embodiment of an implantable medical lead 5108 incross-section with a cut taken down an axial centerline. The lead 5108terminates at a butt joint 5130 where the inner insulation layer 5122,shield 5118, and outer insulation layer 5120 terminate. At this buttjoint 5130, an insulation extension 5132 abuts and is bonded via RFheating, thermal, reflow, or similar processes to the blunt ends of theinner insulation layer 5122, outer insulation layer 5120, and shield5118.

As shown in this example, the shield 5118 terminates at the butt joint5130 rather than farther back within the jacket formed by the inner andouter insulation layers 5122, 5120. The insulation extension 5132 inthis example extends the remainder of the lead 5108 where ringelectrodes 5134 are located. The filars 5124 jumper to their respectivering electrodes via a filar jumper 5136. The lumen may be present withthe filars 5124 being located about the lumen.

The material for the insulation extension 5132 may be selected toprovide more or less stiffness than the inner and outer insulationlayers 5122, 5120, depending upon which end of the lead the butt joint5130 is located. For instance, where the electrode 5134 is on theproximal end of the lead 5108 and is being positioned within the header5106 of the IMD 5102, the insulation extension 5132 may be constructedof a stiffer material. Where the electrode 5134 is on the distal end ofthe lead 5108 and is being steered to the stimulation site within thebody, the insulation extension 5132 may be constructed of a moreflexible material.

Using a stiffer material as the insulation extension 5132 on theproximal end aids in the insertion of the proximal end into the header5106. As a particular example, the outer insulation 5120 may beconstructed of polyurethane having a durometer 55D or similar ratingwhile the insulation extension 5132 may be constructed of a polyurethanehaving a durometer 75D or similar rating.

Using a less stiff material as the insulation extension 5132 on thedistal end aids in the positioning of the distal end at the stimulationsite. As a particular example, the outer insulation 5120 may beconstructed of polyurethane having a durometer 55D or similar ratingwhile the insulation extension 5132 may be constructed of polyurethanehaving a durometer 80A or similar rating.

The gap between the termination of the shield 5118 at the butt joint5130 and the nearest edge of the electrode 5134 is selected to avoid RFproblems. In particular, the distance is selected so that RF coupling isavoided while the unshielded region of the filars 5124 is not overlyexposed to RF. For MRI frequencies that typically range from 43 MHz to128 MHz, a spacing of from 0.5 mm to 10 cm may be acceptable for theseembodiments.

FIG. 21 shows another embodiment of an implantable medical lead 5108 incross-section with a cut taken down an axial centerline. The lead 5108terminates at a scarf joint 5140 where the inner insulation layer 5122,shield 5118, and outer insulation layer 5120 terminate at a wedged cut.At this scarf joint 5140, an insulation extension 5132 that has acomplementary wedged cut abuts and is bonded to the wedged end of theinner insulation layer 5122, outer insulation layer 5120, and shield5118 via RF heating, thermal, reflow or similar processes.

The scarf joint 5140 may be used rather than the butt joint 5130 of FIG.20 because the scarf joint 5140 increases the bonding area. As shown inthis example, the shield 5118 terminates at the scarf joint 5140 ratherthan farther back within the jacket formed by the inner and outerinsulation layers 5122, 5120. The insulation extension 5132 in thisexample extends the remainder of the lead 5108 where ring electrodes5134 are located. The filars 5124 jumper to their respective ringelectrodes via a filar jumper 5136.

Similar to the previous embodiment of FIG. 20, the material for theinsulation extension 5132 in this embodiment of FIG. 4 may be selectedto provide more or less stiffness than the inner and outer insulationlayers 5122, 5120, depending upon which end of the lead the scarf joint5140 is located. For instance, where the electrode 5134 is on theproximal end of the lead 5108 and is being positioned within the header5106 of the IMD 5102, the insulation extension 5132 may be constructedof a stiffer material such as polyurethane with a durometer 75D. Wherethe electrode 5134 is on the distal end of the lead 5108 and is beingsteered to the stimulation site within the body, the insulationextension 5132 may be constructed of a more flexible material such aspolyurethane with a durometer 80A.

The gap between the termination of the shield 5118 at the butt joint5130 and the nearest electrode 5134 is selected to avoid RF problems. Inparticular, the distance is selected so that RF coupling is avoidedwhile the unshielded region of the filars 5124 is not overly exposed toRF. For MRI frequencies that typically range from 43 MHz to 128 MHz,spacing between the edge of the electrode 5134 nearest the scarf joint5140 and the termination of the shield 5118 at the scarf joint 5140 mayrange from 0.5 mm to 10 cm for these embodiments. With the scarf joint5140 of FIG. 21, the spacing between the termination of the shield 5118and the electrode 5134 varies for different locations around thecircumference of the scarf joint 5140, but the shortest spacing ismaintained at 0.5 mm or above and the longest spacing is maintained at10 cm or below.

FIG. 22 shows a set of steps to create the embodiments of FIGS. 20 and21. Initially, a structure including the inner insulation layer 5122,outer insulation layer 5120, and shield 5118 may be provided. The shield5118 has been braided over the inner insulation layer 5122 and then theouter insulation layer 5120 has been positioned and reflowed orotherwise bonded over the inner insulation layer 5122 and the shield5118. To begin construction of the lead 5108 and the butt joint 5130 orscarf joint 5140, the structure is cut to size by making a cut throughthe insulation layers 5120, 5122 and the shield 5118 at a cutting stepS142. For a butt joint 5130, the cut is perpendicular to the axialdimension to create the blunt end. For a scarf joint 5140, the cut is atangle other than 90 degrees to the axial dimension to create the wedgedend.

The insulation extension 5132 is also provided with a complementary endto bond to the lead 5108 to form the butt joint 5130 or scarf joint5140. For the butt joint 5130, the insulation extension 5132 is cutperpendicular to the axial dimension to create the blunt end. For thescarf joint 5140, the insulation extension 5132 is cut at an angle otherthan 90 degrees to the axial dimension to create the wedged end. The twoblunt ends for the butt joint 5130 are brought together and bonded at abonding step S144. Likewise, the two wedged ends for the scarf joint5140 are brought together and bonded at the bonding step S144.

FIG. 23 shows another embodiment of an implantable medical lead 5108 incross-section with a cut taken down an axial centerline. The lead 5108terminates at a lap joint 5150. The lap joint 5150 involves removing anend portion of the outer insulation layer 5120 and applying areplacement outer insulation layer 5152 onto the area of the shield 5118and inner insulation layer 5122 where the outer insulation layer 5120 ismissing. The replacement outer insulation layer 5152 also laps over asection of the insulation extension 5132 and may extend to the nearestelectrode 5134.

As shown, the shield 5118 has been crimped down into the innerinsulation layer 5122 at the region where the outer insulation layer5120 has been removed. Doing so prevents the shield 5118 from bunchingtogether during installation of the outer replacement insulation layer5152. This may be especially the case where the replacement outerinsulation layer 5152 is in the form of tubing that slides into placeover the shield 5118 and inner insulation layer 5122 prior to attachingthe insulation extension 5132. Where the replacement outer insulationlayer 5152 is tubing, once being slid into place, it is reflowed orotherwise bonded to the inner insulation layer 5122. As an alternative,the replacement outer insulation layer 5152 may be injection molded intoplace.

As shown in this example, the shield 5118 terminates at the lap joint5150 rather than farther back within the jacket formed by the inner andouter insulation layers 5122, 5120. The insulation extension 5132 inthis example extends the remainder of the lead 5108 where ringelectrodes 5134 are located. The filars 5124 jumper to their respectivering electrodes via a filar jumper 5136. The lumen may be present insome embodiments with the filars 5124 being located about the lumen.

In this embodiment the replacement outer insulation layer 5152 may beconstructed of a material that differs in stiffness from the outerinsulation layer 5120 depending upon which end of the lead 5108 the lapjoint 5150 is located. For instance, where the electrode 5134 is on theproximal end of the lead 5108 and is being positioned within the header5106 of the IMD 5102, the replacement outer insulation layer 5152 may beconstructed of a stiffer material such as durometer 75D polyurethane.Where the electrode 5134 is on the distal end of the lead 5108 and isbeing steered to the stimulation site within the body, the replacementouter insulation layer 5152 may be constructed of a more flexiblematerial such as 80A polyurethane.

In this embodiment, like that of the previous ones, the material for theinsulation extension 5132 may also be selected to provide more or lessstiffness than the inner and outer insulation layers 5122, 5120,depending upon which end of the lead the lap joint 5150 is located. Forinstance, where the electrode 5134 is on the proximal end of the lead5108 and is being positioned within the header 5106 of the IMD 5102, theinsulation extension 5132 may be constructed of a stiffer material suchas durometer 75D polyurethane. Where the electrode 5134 is on the distalend of the lead 5108 and is being steered to the stimulation site withinthe body, the insulation extension 5132 may be constructed of a moreflexible material such as 80A polyurethane.

The gap between the termination of the shield 5118 at the lap joint 5150and the nearest electrode 5134 is also selected to avoid RF problems.For MRI frequencies, a spacing of from 0.5 mm to 10 cm may be acceptablefor these embodiments. FIG. 24 shows one example of a set of steps thatcreate the lap joint 5150 of FIG. 23. Initially, a structure includingthe inner insulation layer 5122, outer insulation layer 5120, and shield5118 may be provided. The shield 5118 has been braided over the innerinsulation layer 5122 and then the outer insulation layer 5120 has beenpositioned and reflowed or otherwise bonded over the inner insulationlayer 5122 and the shield 5118. To begin construction of the lead 5108and the lap joint 5150, the structure is cut to size by making a cutthrough the insulation layers 5120, 5122 and the shield 5118 at acutting step S154. For a lap joint 5150, this first cut is perpendicularto the axial dimension to create a blunt end.

Once cut to size, the outer insulation layer 5120 is then ablated bysome distance to expose the shield 5118 and the inner insulation layer5122 at an ablating step S156. Ablation may be done using tools such asan excimer laser which can very precisely ablate to expose the shield5118. The length of the outer insulation layer 5120 to be ablated mayvary, but an illustrative range is from 0.25 centimeters (cm) to 5 cm.

Once ablation is complete, the next step may vary. The replacement outerinsulation layer 5152 may be installed in various manners such as byreflowing tubing or by injection molding. If by injection molding, thenthe next step may be either a crimping step S158 or an injecting stepS162. If by reflowing tubing, then it may be helpful to proceed to thecrimping step S158 after ablating.

At the crimping step S158, the shield 5118 is crimped so as to sink downinto the inner insulation layer 5122 at the area where the outerinsulation layer 5120 has been removed. If a ring or other tool is usedto crimp the shield 5118 into the inner insulation layer 5122, the ringor other tool may then be removed. Where the replacement outerinsulation layer 5152 is being installed as tubing that is reflowed,then the next step is tubing step S160. Where the replacement outerinsulation layer 5152 is being installed by injection molding, then thenext step is injecting step S162.

At the tubing step S160, the tubing is slid onto the inner insulationlayer 5122 and over the shield 5118 at the area where the outerinsulation layer 5120 has been removed and where the shield 5118 hasbeen crimped down. The tubing extends beyond the end of the innerinsulation layer 5122 so that it may eventually be bonded to theinsulation extension 5132. The tubing is reflowed, RF heated, etc. tobond to the inner insulation layer 5122 and to the end of the outerinsulation layer 5120 where the ablating stopped to form the replacementouter insulation layer 5152. Contemporaneously or sequentially, theinsulation extension 5132 is bonded in place at the blunt end of theinner insulation layer 5122 and to the tubing of the replacement outerinsulation layer 5152 that extends beyond the inner insulation layer5122 at a bonding step S164. This tubing may be reflowed, RF heated,etc. onto the insulation extension 5132.

Returning to the injecting step S162, in the scenario where thereplacement outer insulation layer 5152 is to be injection molded, thenthe injecting step 5126 takes place either after the ablating step S156or after the crimping step S158. Material such as the desiredpolyurethane is injected onto the inner insulation layer 5122 and theshield 5118 to form the replacement outer insulation layer 5152.Contemporaneously, the insulation extension 5132 is bonded to the innerinsulation layer 5122 and to the replacement outer insulation layer 5152at the bonding step S164.

Alternative manners of creating the lap joint 5150 may also be used. Forinstance, the structure of the outer insulation layer 5120, innerinsulation layer 5122, and shield 5118 may be bonded to the insulationextension 5132 via a butt joint. Then, the area where the replacementouter insulation layer 5152 will be positioned that is currentlyoccupied by the outer insulation layer 5120 is ablated. The insulationextension 5132 is also ablated at the same or similar depth as the outerinsulation layer 5120. The replacement outer insulation layer 5152 maythen be injection molded or shrunk into position at the ablation site.

FIG. 25 shows an embodiment with an additional feature that may beincluded for the lap joint 5150. To further protect the termination ofthe shield 5118 from fraying or migrating, the wire ends of the shield5118 may be capped with a ring 5166. The ring 5166 may be metal,plastic, or similar materials. In this example, a region 5168 of theinner insulation layer 5122 has been ablated to allow the ring to bepositioned over the ends of the wires of the shield 5118.

FIG. 26 shows an embodiment with an additional feature that may beincluded for the butt or scarf joints 5130, 5140. To further protect thetermination of the shield 5118 from fraying or migrating, the wire endsof the shield 5118 may be capped with a ring 5170. Similar to the lapjoint scenario, the ring 5170 may be metal, plastic, or similarmaterials. In this example, a region 5172 of the outer insulation layer5120 has been ablated to allow the ring 5170 to be positioned over theends of the wires of the shield 5118, and then this region 5172 may befilled using a reflow or injection molding of the polyurethane or otherpolymer.

FIG. 27 shows an embodiment with an additional feature that may beincluded for a joint 5176, which may be of various types such as thebutt, scarf, or lap joints 5130, 5140, and 5150. At the joint 5176, theouter insulation layer 5120 of the lead 5108 encounters another layer5178. This layer 5178 may be the insulation extension 5132 and/or thereplacement outer insulation layer 5152. In either case, wires of theshield 5118 may partially extend into the layer 5178. However, prior tobonding the layer 5178 to the layers 5120 or 5122, the ends of the wiresof the shield 5118 may be individually folded over as shown in FIG. 27.In this manner, the folded over ends are less likely to fray andmigrate.

FIG. 28 shows an embodiment with another feature that may be includedfor a joint at the termination of the shield 5118 to assist in holdingthe bond between the inner insulation layer 5122 and the insulationextension 5132 in place. In this example, a lap joint 5150 is shown, butit will be appreciated that this feature may be applicable to otherjoints as well including butt and scarf joints 5130, 5140. Here, thereplacement outer insulation layer 5152 may be tubing that is providedwith barbs 5151 that extend toward the inner insulation layer 5122 andthe shield 5118.

During reflow, the barbs may sink into the inner insulation layer 5122as the inner insulation layer 5122 softens more so than the barbs 5151,and the replacement outer insulation layer 5152 descends into position.The barbs 5151 may also sink into the insulation extension 5132 oncereflow or other bonding is attempted after the insulation extension 5132has been inserted to provide extra grip between the replacement outerinsulation layer 5152 and the insulation extension 5132. The barbs 5151then provide extra grip between the inner insulation layer 5122 and theinsulation extension 5132 particularly during axial tension. Rather thanincorporating the barbs into the replacement outer tubing 5152 of thelap joint example, a separate barbed ring may be positioned on the innerinsulation layer 5122 and then the replacement outer insulation layer5152 is reflowed or otherwise bonded into place.

FIG. 29 shows an embodiment with another feature that may be includedfor a joint at the termination of the shield 5118 to assist in holdingthe bond between the inner insulation layer 5122 and the insulationextension 5132 in place. In this example, a lap joint 5150 is shown, butit will be appreciated that this feature may be applicable other jointsas well including butt and scarf joints 5130, 5140. Here, a barbed ring5153 is positioned inside of the inner insulation layer 5122 and isforced to expand radially until the barbs of the barbed ring 5153 sinkinto the inner insulation layer 5122. The barbs of the barbed ring 5153may also sink into the inside of the insulation extension 5132. Thebarbed ring 5153 provides extra grip between the inner insulation layer5122 and the insulation extension 5132 especially during axial tension.This barbed ring 5153 feature may also be used in conjunction with thebarbs 5151 shown in FIG. 28.

Embodiments as disclosed in relation to FIGS. 30-48 also provide fortermination of a radio frequency (RF) shield present within animplantable medical lead for use with an implantable medical device(IMD). The shield may be terminated in various ways such as byterminating at a joint to an insulation extension where one or moremetal connectors are present in various configurations to provide aground path for the shield. Furthermore, the shield termination mayinclude features such as a shield wires with folded over ends, or barbsbetween the insulation layers.

FIG. 30 shows an example of an implantable medical system 6100 thatincludes an IMD 6102 coupled to a lead 6108. The IMD 6102 includes ametal can 6104, typically constructed of a medical grade titanium, suchas grades 1-4, 5 or 9 titanium, or similar other biocompatiblematerials. The IMD 6102 includes a header 6106 typically constructed ofmaterials such as polysulfone or polyurethane, that is affixed to themetal can 6104. The header 6106 is shown transparently for purposes ofillustration. The header 6106 provides a structure for securing the lead6108 to the IMD 6102 and for establishing electrical connectivitybetween circuitry of the IMD 6102 and electrodes of the lead 6108.

The lead 6108 includes electrodes 6116 on a distal end that arepositioned at a stimulation site within a patient. The lead alsoincludes ring connectors 6110 on a proximal end that is positionedwithin the header 6106. The ring connectors 6110 make physical contactwith electrical connections 6111 within the header. The electricalconnections 6111 may include a metal contact that the ring connector6110 rests against upon being inserted into the header 6106 where a wireextends from the metal contact into the can 6104 where the circuitry ishoused. Signals applied by the IMD 6102 to the ring connectors 6110 areconducted through the lead 6108 to the electrodes 6116 to provide thestimulation therapy to the patient.

The lead 6108 is secured in the header 6106 such as by a set screw block6112 within the header 6106 that allows at least one set screw 6114 tobe tightened against at least one of the ring connectors 6110. A shield6118 as shown in FIGS. 31A and 31B may be grounded to the body along oneor more points down the length of the lead from the IMD 6102 via groundrings and/or the shield 6118 may be grounded at the can 6104 of the IMD6102 of FIG. 30.

Regardless of the manner of grounding, the shield 6118 terminates on oneend near the proximal end and on the opposite end near the distal end ofthe lead 6108. At the termination point, shields having multiple metalwires such as braided shields are subject to fraying and shield wiremigration. Preventing the shield wire from fraying and/or migrating tothe tissue or to stimulation conductors within the lead 6108 may bedesirable to prevent RF energy captured by the shield 6118 from beingdirected onto a small area of tissue via an electrode or exposed shieldwire.

FIGS. 31A and 31B show an example of the lead 6108, where a shield 6118is present. An outer insulation layer 6120 of a lead jacket is showntransparently in FIG. 31A for purposes of illustrating the shield 6118.The shield 6118 blocks at least some RF energy from directly coupling toconductive filars 6124 that are present within the lead 6108. Theconductive filars 6124 extend the length of the lead and interconnectthe proximal ring connectors 6110 to the distal electrodes 6116 so thatstimulation signals are conducted from the proximal end to the distalend of the lead 6108.

As shown in FIG. 31A, the shield 6118 of this example is a braidedcollection of metal wires. The metal wires may be constructed of variousmaterials such as titanium, tantalum, niobium, platinum-iridium alloy,platinum, palladium, gold, stainless steel, and their alloys, or othermetals. It may be desired to utilize a biocompatible metal for theshield 6118, particularly for embodiments where a portion of the shield6118 may be exposed for purposes of grounding. While the shield 6118 isshown as a braid, other shield configurations may be chosen particularlywhere flexibility is not an issue such as a foil strip wrapped about thelead 6108 in an overlapping manner or an outer layer 6120 that isheavily doped with conductive particles.

As shown in FIG. 31B, the shield 6118 may be embedded within the jacketof the lead 6108. One manner of constructing the lead 6108 with theshield 6118 is to provide an inner insulation layer 6122 of the jacketthat encloses the filars 6124 and any additional insulation layer 6126,such as polytetrafluoroethylene (PTFE) that may surround each filar6124. The shield 6118 may then reside on the outer portion of the innerinsulation layer 6122, and the outer insulation layer 6120 may thenenclose the shield 6118. The outer insulation layer 6120 may be addedover the shield 6118 and shrunk in place or may be extruded over theshield 6118. The outer jacket 6120 maybe added over the braid 6118, orit may be extruded over the braid.

For embodiments where it is desirable for the shield 6118 to RF coupleto tissue, typically as a capacitive coupling, in addition to groundingat the can or along the lead, the amount of the outer jacket layer 6120covering the shield 6118 may be relatively thin, such as on the order of0.5 to 5 mils. Where the shield 6118 grounds at one or more specificlocations along its length, via a direct current coupling or acapacitive coupling, the shield 6118 may be located further from theouter surface of the lead 6108.

The inner and outer insulation layers 6122, 6120 of the jacket may beconstructed of the same or similar materials such as various flexibleand biocompatible polymers, examples of which are polyurethanes andsilicones. A lumen 6128 may be included inside of the inner jacket 6122around which the insulated filars 6124 are coiled or otherwisepositioned. The lumen 6128 may be useful, particularly for percutaneousleads 6108, to allow a stylet to be inserted for purposes of pushing andsteering the lead 6108 into the desired position within the patient.

FIG. 32 shows an embodiment of an implantable medical lead 6108 incross-section with a cut taken down an axial centerline. The lead 6108includes a butt joint 6130 where the inner insulation layer 6122 andshield 6118 terminate. The outer insulation 6120 terminates prior to thebutt joint 6130 to expose the shield 6118 and inner insulation layer6122. A metal connector 6131 is positioned over the shield 6118 andinner insulation layer 6122 and abuts the end of the outer insulationlayer 6120. At the butt joint 6130, an insulation extension 6132 abutsand is bonded to the blunt end of the inner insulation layer 6122,shield 6118, and metal connector 6131 such as via reflow or injectionmolding.

As shown in this example, the shield 6118 terminates at the butt joint6130 rather than farther back within the jacket formed by the inner andouter insulation layers 6122, 6120. The insulation extension 6132 inthis example extends the remainder of the lead 6108 where ringconnectors 6134 are located on the proximal end at a separate from thenearest connector ring ranging from about 0.5 millimeters to about 10centimeters. The filars 6124 jumper to their respective ring connectorsvia a filar jumper 6136. The lumen may be present in some embodimentswith the filars 6124 being located about the lumen.

The material for the insulation extension 6132 may be selected toprovide a different amount of stiffness than the inner and outerinsulation layers 6122, 6120. For instance, the insulation extension6132 may be constructed of a stiffer material to aid in the insertion ofthe proximal end into the header 6106. As a particular example, theouter insulation 6120 may be constructed of polyurethane having adurometer 55D or similar rating while the insulation extension 6132 maybe constructed of a polyurethane having a durometer 75D or similarrating.

The shield 6118 may be terminated with an exposed metal connector 6131at a butt joint on the distal end so long as no terminating ground ringis present at the proximal end to thereby avoid stimulation induced bymagnetic gradients. In such a case, the insulation extension may have adurometer rating similar to the outer layer 6120 but may instead beconstructed of polyurethane having a durometer 80A or similar rating.

The metal connector 6131 is separated from the distal electrode by atleast 0.5 mm up to 10 cm for some body locations, to avoid excessive RFcoupling to the distal electrode, with 2 mm being one example of spacingthat provides adequate filar coverage with insignificant coupling to thedistal electrode. Where the distal end is located in a high RF intensityarea such as just under the skin for peripheral nerve stimulation, thenthe distance may be kept smaller, such as less than 2 cm to avoidoverexposure of the filars 6124.

FIG. 33 shows another embodiment of an implantable medical lead 6108 incross-section with a cut taken down an axial centerline. The lead 6108terminates at a scarf joint 6140 where the inner insulation layer 6122and shield 6118 terminate at a wedged cut. The outer insulation 6120terminates prior to the scarf joint 6140 to expose the shield 6118 andinner insulation layer 6122. A metal connector 6131 is positioned overthe shield 6118 and inner insulation layer 6122 and abuts the end of theouter insulation layer 6120. At this scarf joint 6140, an insulationextension 6132 that has a complementary wedged cut abuts and is bondedto the wedged end of the inner insulation layer 6122, shield 6118, andmetal connector 6131 such as via reflow or injection molding.

The scarf joint 6140 may be used rather than the butt joint 6130 of FIG.32 because the scarf joint 6140 has an increased bond area. As shown inthis example, the shield 6118 terminates at the scarf joint 6140 ratherthan farther back within the jacket formed by the inner and outerinsulation layers 6122, 6120. The insulation extension 6132 in thisexample extends the remainder of the lead 6108 where ring connectors6134 are located on the proximal end. The filars 6124 jumper to theirrespective ring connectors via a filar jumper 6136.

Similar to the previous embodiment of FIG. 32, the material for theinsulation extension 6132 in this embodiment of FIG. 33 may be selectedto provide a different stiffness than the inner and outer insulationlayers 6122, 6120. For instance, the insulation extension 6132 may beconstructed of a stiffer material such as polyurethane with a durometer75D.

The metal connector 6131 may be included on either the proximal ordistal end to terminate the shield 6118 as discussed above. Theseparation of the metal connector 6131 to the distal electrode orproximal connector ring may also be in accordance with the separation asdiscussed above.

FIG. 34 shows a set of steps to create the embodiments of FIGS. 32 and33. Initially, a structure including the inner insulation layer 6122,outer insulation layer 6120, and shield 6118 may be provided. The shield6118 has been braided over the inner insulation layer 6122 and then theouter insulation layer 6120 has been positioned and reflowed orotherwise bonded over the inner insulation layer 6122 and the shield6118. To begin construction of the lead 6108 and the butt joint 6130 orscarf joint 6140, the structure is cut to size by making a cut throughthe insulation layers 6120, 6122 and the shield 6118 at a cutting step6142. For a butt joint 6130, the cut is perpendicular to the axialdimension to create the blunt end. For a scarf joint 6140, the cut is atangle other than 90 degrees to the axial dimension to create the wedgedend.

The end portion of the outer insulation layer 6120 is ablated to revealthe shield 6118 at ablating step 6144. The metal connector 6131, such asa ring connector, may then be crimped or welded onto the shield 6118 atcrimping step 6146.

The insulation extension 6132 is bonded to the lead 6108 to form thebutt joint 6130 or scarf joint 6140 at a bonding step 6148. For the buttjoint 6130, the insulation extension 6132 is cut perpendicular to theaxial dimension to create the blunt end. For the scarf joint 6140, theinsulation extension 6132 is cut at an angle other than 90 degrees tothe axial dimension to create the wedged end. The two blunt ends for thebutt joint 6130 are brought together and bonded at a bonding step 6148.Likewise, the two wedged ends for the scarf joint 6140 are broughttogether and bonded at the bonding step 6148.

FIG. 35 shows another embodiment of an implantable medical lead 6108 incross-section with a cut taken down an axial centerline. The lead 6108includes a lap joint 6150 where the inner insulation layer 6122 and theshield 6118 terminate. The lap joint 6150 involves removing an endportion of the outer insulation layer 6120 sufficient to allow space forthe metal connector 6131 and a replacement outer insulation layer 6152to lap over the area of the shield 6118 and inner insulation layer 6122where the outer insulation layer 6120 is missing. The metal connector6131 abuts the end of the outer insulation layer 6120. The replacementouter insulation layer 6152 abuts the metal connector 6131, laps over asection of the insulation extension 6132, and may extend to the nearestelectrode 6134.

As shown, the shield 6118 has been crimped down into the innerinsulation layer 6122 at the region where the outer insulation layer6120 has been removed. Doing so prevents the shield 6118 from bunchingtogether during installation of the outer replacement insulation layer6152. This may be especially the case where the replacement outerinsulation layer 6152 is in the form of tubing that slides into placeover the shield 6118 and inner insulation layer 6122 prior to attachingthe insulation extension 6132. Where the replacement outer insulationlayer 6152 is tubing, once being slid into place, it is reflowed orotherwise bonded to the inner insulation layer 6122. As an alternative,the replacement outer insulation layer 6152 may be injection molded intoplace.

As shown in this example, the shield 6118 terminates at the lap joint6150 rather than farther back within the jacket formed by the inner andouter insulation layers 6122, 6120. The insulation extension 6132 inthis example extends the remainder of the lead 6108 where ringconnectors 6134 are located at the proximal end. The filars 6124 juniperto their respective ring connectors via a filar juniper 6136. The lumenmay be present in some embodiments with the filars 6124 being locatedabout the lumen.

In this embodiment the replacement outer insulation layer 6152 may beconstructed of a material that differs in stiffness from the outerinsulation layer 6120. For instance, the replacement outer insulationlayer 6152 may be constructed of a stiffer material such as durometer75D polyurethane. In this embodiment, like that of the previous ones,the material for the insulation extension 6132 may also be selected toprovide a different stiffness than the inner and outer insulation layers6122, 6120. For instance, the insulation extension 6132 may also beconstructed of a stiffer material such as durometer 75D polyurethane.

The metal connector 6131 may be included on either the proximal ordistal end to terminate the shield 6118 as discussed above. Theseparation of the metal connector 6131 to the distal electrode orproximal connector ring may also be in accordance with the separation asdiscussed above.

FIG. 36 shows one example of a set of steps that create the lap joint6150 of FIG. 35. Initially, a structure including the inner insulationlayer 6122, outer insulation layer 6120, and shield 6118 may beprovided. The shield 6118 has been braided over the inner insulationlayer 6122 and then the outer insulation layer 6120 has been positionedand reflowed or otherwise bonded over the inner insulation layer 6122and the shield 6118. To begin construction of the lead 6108 and the lapjoint 6150, the structure is cut to size by making a cut through theinsulation layers 6120, 6122 and the shield 6118 at a cutting step 6154.For a lap joint 6130, this first cut is perpendicular to the axialdimension to create a blunt end.

Once cut to size, the outer insulation layer 6120 is then ablated bysome distance to expose the shield 6118 and the inner insulation layer6122 at an ablating step 6156. Ablation may be done using tools such asan excimer laser which can very precisely ablate to expose the shield6118. The length of the outer insulation layer 6120 to be ablated issufficient to allow for the metal connector 6131 as well as the amountof the replacement outer insulation layer 6152 that laps onto the innerinsulation layer 6122. This length of ablation of the outer insulationlayer 6120 may vary but an illustrative range is from 0.25 centimeters(cm) to 5 cm.

Once ablation is complete, the metal connector 6131 may then be put inposition over the inner insulation layer 6122 and shield 6118. The metalconnector 6131 is crimped or welded to the shield 6118 while abuttingthe end of the outer insulation layer 6120 at a crimping step 6158.

Once the metal connector 6131 is installed, the next step may vary. Thereplacement outer insulation layer 6152 may be installed in variousmanners such as by reflowing tubing or by injection molding. If byinjection molding, then the next step may be either a crimping step 6160or an injecting step 6164. If by reflowing tubing, then it may behelpful to proceed to the crimping step 6160 after ablating.

At the crimping step 6160, the portion of the shield 6118 that isexposed beyond the metal connector 6131 is crimped so as to sink downinto the inner insulation layer 6122. If a ring or other tool is used tocrimp the shield 6118 into the inner insulation layer 6122, the ring orother tool may then be removed. Where the replacement outer insulationlayer 6152 is being installed as tubing that is reflowed, then the nextstep is tubing step 6162. Where the replacement outer insulation layer6152 is being installed by injection molding, then the next step isinjecting step 6164.

At the tubing step 6162, the tubing is slid onto the inner insulationlayer 6122 and over the shield 6118 at the area where the outerinsulation layer 6120 has been removed and where the shield 6118 hasbeen crimped down. The tubing extends beyond the end of the innerinsulation layer 6122 so that it may eventually be bonded to theinsulation extension 6132. The tubing is reflowed or otherwise bonded tothe inner insulation layer 6122 and to abut the end of the metalconnector 6131. Contemporaneously, the insulation extension 6132 isbonded in place at the blunt end of the inner insulation layer 6122 andto the tubing of the replacement outer insulation layer 6152 thatextends beyond the inner insulation layer 6122 at a bonding step 6166.This tubing may be reflowed or otherwise bonded onto the insulationextension 6132.

Returning to the injecting step 6164, in the scenario where thereplacement outer insulation layer 6152 is to be injection molded, thenthe injecting step 6164 takes place either after the crimping step 6158or after the crimping step 6160. Material such as the desiredpolyurethane is injected onto the inner insulation layer 6122 and theshield 6118 to form the replacement outer insulation layer 6152.Contemporaneously, the insulation extension 6132 is bonded to the innerinsulation layer 6122 and to the replacement outer insulation layer 6152at the bonding step 6166.

Alternative manners of creating the lap joint 6150 may also be used. Forinstance, the structure of the outer insulation layer 6120, innerinsulation layer 6122, and shield 6118 may be bonded to the insulationextension 6130 via a butt joint. Then, the area where the metalconnector 6131 and replacement outer insulation layer 6152 will bepositioned that is currently occupied by the outer insulation layer 6120is ablated. The insulation extension 6132 is also ablated at the same orsimilar depth as the outer insulation layer 6120. The metal connector6131 may then be positioned, and the replacement outer insulation layer6152 may then be injection molded or shrunk into position at theablation site.

FIG. 37 shows another embodiment of an implantable medical lead 6108 incross-section with a cut taken down an axial centerline. The lead 6108includes a joint between the inner insulation layer 6122 and theinsulation extension 6132 where the inner insulation layer 6122 and theshield 6118 terminate. An inner metal connector 6172 is positionedaround the inner insulation layer and an outer metal connector 6174 ispositioned around the inner metal connector 6172. A portion of theshield 6118 is located between the inner metal connector 6172 and theouter metal connector 6174 such that a robust physical and electricalconnection is established to the shield 6118.

In this example, the shield 6118 is braided after the inner metalconnector 6172 has been positioned so that the braid of the shield 6118laps over the inner metal connector 6172. The outer insulation layer6120 terminates short of the end of the shield 6118 and inner insulationlayer 6122. This may be achieved by ablating the outer insulation layer6120 where it has been previously extruded over the shield and innermetal connector 6172.

As shown in this example, the shield 6118 terminates between the metalconnectors 6172, 6174 rather than farther back within the jacket formedby the inner and outer insulation layers 6122, 6120. The insulationextension 6132 in this example extends the remainder of the lead 6108where ring connectors 6134 are located at the proximal end. The filars6124 jumper to their respective ring connectors via a filar jumper 6136.The lumen may be present in some embodiments with the filars 6124 beinglocated about the lumen.

The metal connectors 6172, 6174 may be included on either the proximalor distal end to terminate the shield 6118 as discussed above. Theseparation of the metal connectors 6172, 6174 to the distal electrode orproximal connector ring may also be in accordance with the separation asdiscussed above for connector ring 6131.

FIG. 38 shows an alternative manner of attaching the outer metalconnector. Rather than ablate the outer insulation layer 6120 at thearea where the shield 6118 and inner metal connector 6172 are located,an outer metal connector 6176 having features such as teeth that canpenetrate through the outer insulation layer 6120 is used. The outermetal connector 6176 is crimped in place so that the features penetratethrough the outer insulation layer 6120 to reach the shield 6118 and theinner metal connector 6172 and establish the physical and electricalconnection.

FIG. 39 shows a similar embodiment to that of FIG. 37 where the leadincludes the inner metal connector 6172 and the outer metal connector6174. However, in this example, the shield 6118 does not terminatebetween the metal connectors 6172, 6174 but a portion 6119 of the shield6118 continues beyond those connectors 6172, 6174 to extend over theremaining portion of the inner insulation layer 6122. This portion 6119of the shield 6118 may be crimped into a sunken position within theinner insulation layer 6122. A replacement outer insulation layer 6152may be bonded over the portion 6119 of the shield 6118 to form a lapjoint. The insulation extension 6132 may then be bonded to the innerinsulation layer 6122 and the replacement outer insulation layer 6152.The insulation extension 6132 in this example extends the remainder ofthe lead 6108 where ring connectors 6134 are located at the proximalend. The filars 6124 jumper to their respective ring connectors via afilar jumper 6136. The lumen may be present in some embodiments with thefilars 6124 being located about the lumen.

The metal connectors 6172, 6174 may be included on either the proximalor distal end to terminate the shield 6118 as discussed above. Theseparation of the metal connectors 6172, 6174 as well as any portion ofthe shield 6118 extending beyond the metal connectors 6172, 6174 to thedistal electrode or proximal connector ring may also be in accordancewith the separation as discussed above.

FIG. 40 shows a similar embodiment to that of FIG. 37 where the leadincludes the inner metal connector 6172 and the outer metal connector6174. However, in this example, the inner metal connector 6172 does notwrap around the outside of the inner insulation layer 6122 but insteadis embedded within the inner insulation layer 6122 so as to provide aflush surface for the shield 6118 to be braided upon. The shield 6118 islocated between this inner metal connector 6172 and the outer metalconnector 6174. In this example, the metal connectors 6172, 6174together with the inner insulation layer 6122 form a butt joint with theinsulation extension 6132.

The insulation extension 6132 is bonded to the inner insulation layer6122 and abuts the metal connectors 6172, 6174. The insulation extension6132 in this example extends the remainder of the lead 6108 where ringconnectors 6134 are located at the proximal end. The filars 6124 jumperto their respective ring connectors via a filar jumper 6136. The lumenmay be present in some embodiments with the filars 6124 being locatedabout the lumen.

The metal connectors 6172, 6174 may be included on either the proximalor distal end to terminate the shield 6118 as discussed above. Theseparation of the metal connectors 6172, 6174 to the distal electrode orproximal connector ring may also be in accordance with the separation asdiscussed above.

FIG. 41 shows one example of a set of steps that create the shieldtermination of FIGS. 37-40. The inner metal connector 6172 is positionedon the inner insulation layer 6122 or embedded at the end at a connectorstep 6182. The shield 6118 is braided onto the inner insulation layer6122 and over the inner metal connector 6172 at a braiding step 6184.The outer insulation layer 6120 is bonded by reflow or another processonto the inner insulation layer 6122 over the shield 6118 and over theinner metal connector 6172 such as by a reflowing step 6186.

At this point, preparation is made for the outer metal connector 6174.In one example, the outer insulation layer is ablated at an ablatingstep 6188 and then the outer metal connector is crimped or welded ontothe exposed shield 6118 at the overlap to the inner metal connector 6172at a crimping step 6190. Alternatively, the inner metal connector 6176having the sharp features is crimped onto the outer insulation layer6120 with the sharp features penetrating to the shield 6118 and theinner metal connector 6172 at a crimping step 6192. The insulationextension 6132 is then bonded to the inner insulation layer 6122 at abonding step 6194.

FIG. 42 shows a similar embodiment to that of FIG. 37 where the leadincludes the inner metal connector 6172 and the outer metal connector6174. However, in this example, the inner metal connector 6172 does notwrap around the outside of the inner insulation layer 6122 prior to theshield 6118 being braided. Instead, the shield 6118 is braided over theinner insulation layer 6122 and the inner metal connector 6172 is thencrimped or welded onto the shield 6118. The shield 6118 may be sunkeninto the inner insulation layer 6122 in the area where the inner metalconnector 6172 is positioned.

The shield 6118 inverts as a whole at an inversion 6123 so that aportion 6121 of the shield 6118 laps over the inner metal connector6172. The outer metal connector 6174 may then be crimped or welded inplaced about the portion 6121 and the inner metal connector 6172. Arobust electrical and physical termination of the shield 6118 occursbetween the metal connectors 6172, 6174. The inversion 6123 may provideadditional benefits for the shield 6118, such as reducing any RF energyleakage that might otherwise occur at a blunt end of the shield 6118.

The insulation extension 6132 is bonded to the inner insulation layer6122 and abuts the metal connectors 6172, 6174. The insulation extension6132 in this example extends the remainder of the lead 6108 where ringconnectors 6134 are located at the proximal end. The filars 6124 jumperto their respective ring connectors via a filar jumper 6136. The lumenmay be present in some embodiments with the filars 6124 being locatedabout the lumen.

The metal connectors 6172, 6174 may be included on either the proximalor distal end to terminate the shield 6118 as discussed above. Theseparation of the metal connectors 6172, 6174 to the distal electrode orproximal connector ring may also be in accordance with the separation asdiscussed above.

FIG. 43 shows one example of a set of steps that create the shieldtermination of FIG. 42. The outer insulation layer 6120, innerinsulation layer 6122, and shield 6118 are cut to form a blunt end at acutting step 6202. A portion of the outer insulation layer 6120 is thenablated to reveal the shield 6118 and inner insulation layer 6122 at anablating step 6204. The inner metal connector 6172 is positioned on theshield 6118 and around the inner insulation layer 6122 with a portion ofthe shield 6118 and the inner insulation layer 6122 extending beyond themetal connector 6172 at a connector step 6206. The shield 6118 isinverted as a whole and lapped onto the inner metal connector at afolding step 6208.

At this point, the outer metal connector is crimped or welded onto theexposed shield 6118 at the overlap to the inner metal connector 6172 ata crimping step 6210. Alternatively, the outer metal connector 6176having the sharp features is crimped onto the outer insulation layer6120 with the sharp features penetrating to the shield 6118 and theinner metal connector 6172. The insulation extension 6132 is then bondedto the inner insulation layer 6122 at a bonding step 6212.

FIG. 44 shows another embodiment of an implantable medical lead 6108 incross-section with a cut taken down an axial centerline. The lead 6108includes a joint between the inner insulation layer 6122 and theinsulation extension 6132 where the inner insulation layer 6122terminates. In this example, the shield 6118 does not remain braidedupon the inner insulation layer 6122. Instead, a metal connector 6131 ispositioned on the inner insulation layer 6122 and a portion 6125 of theshield 6118 is braided onto the metal connector 6131. The outerinsulation layer 6120 is positioned over the braid 6118 up to the metalconnector 6131 where the braid 6118 exits the outer insulation layer6120 when lapping onto the metal connector 6131.

The portion 6125 may be exposed outside of the lead 6108 as a result oflapping onto the metal connector 6131. However, for embodiments wherethe metal connector 6131 is for insertion into the header 6106 of theIMD 6102, the exposure may occur immediately at the exit to the header6106 or nearby the header seal. To the extent tissue in-growth is to beavoided in that area, an insulation ring 6216 of material the same as orsimilar to the outer insulation layer 6120 may be reflowed or otherwisebonded over the portion 6125.

As shown in this example, a replacement outer insulation layer 6152 maybe present to form a lap joint between the inner insulation layer 6122and the insulation extension 6132. The insulation extension 6132 in thisexample extends the remainder of the lead 6108 where ring connectors6134 are located at the proximal end. The filars 6124 jumper to theirrespective ring connectors via a filar jumper 6136. The lumen may bepresent in some embodiments with the filars 6124 being located about thelumen.

The metal connector 6131 may be included on either the proximal ordistal end to terminate the shield 6118 as discussed above. Theseparation of the metal connector 6131 to the distal electrode orproximal connector ring may also be in accordance with the separation asdiscussed above.

FIG. 45 shows one example of a set of steps that create the shieldtermination of FIG. 44. The metal connector 6131 is positioned on theinner insulation layer 6122 at a connector step 6220. The shield 6118 isbraided onto the inner insulation layer 6122 and over the metalconnector 6131 at a braiding step 6222. The outer insulation layer 6120is bonded by reflow or another process onto the inner insulation layer6122 over the shield 6118 up to the metal connector 6131 such as by areflowing step 6224. The insulation ring 6216 may then be reflowed orinjection molded over the braid portion 6125 on the metal connector 6131at a bonding step 6226.

FIG. 46 shows another embodiment of an implantable medical lead 6108 incross-section with a cut taken down an axial centerline. The lead 6108includes a joint between the inner insulation layer 6122 and theinsulation extension 6132 where the inner insulation layer 6122terminates. In this example, the shield 6118 does not remain braidedupon the inner insulation layer 6122. Instead, a tapered ablation iscreated through the outer insulation layer 6120 and inner insulationlayer 6122 and the shield 6118 exits the outer insulation layer 6120 andseparates from the inner insulation layer 6122 at the taper.

A metal connector 6232 with a threaded taper 6234 is threaded onto thetaper of the inner and outer insulation layers 6122, 6120. The threadedtaper 6234 bites into the inner and outer insulation layers 6122, 6120to provide a sturdy physical connection. The shield 6118 passes throughthe metal connector 6232 to an opposite side where an opposite taper ispresent. There, the shield 6118 terminates while being positioned firmlybetween the taper of the metal connector 6232 and a taper of an innermetal connector 6236 that is positioned about the insulation extension6132.

The insulation extension 6132 in this example extends the remainder ofthe lead 6108 where ring connectors 6134 are located at the proximalend. The filars 6124 jumper to their respective ring connectors via afilar jumper 6136. The lumen may be present in some embodiments with thefilars 6124 being located about the lumen.

The metal connectors 6232, 6236 may be included on either the proximalor distal end to terminate the shield 6118 as discussed above. Theseparation of the metal connectors 6232, 6236 to the distal electrode orproximal connector ring may also be in accordance with the separation asdiscussed above.

FIG. 47 shows one example of a set of steps that create the shieldtermination of FIG. 46. The inner metal connector 6236 is positioned atthe end of the inner insulation layer 6122 at a connector step 6242. Theshield 6118 is braided onto the inner insulation layer 6122 and over theinner metal connector 6236 at a braiding step 6244. The outer insulationlayer 6120 is bonded by reflow or another process onto the innerinsulation layer 6122 over the shield 6118 such as by a reflowing step6246.

The inner and outer insulation layers 6122, 6120 are ablated to form thetaper and expose the shield 6118 at an ablating step 6248. The outermetal connector 6232 is then placed into position over the inner metalconnector 6236 and the taper of the inner and outer insulation layers6122, 6120 at a connector step 6250. Here, the outer metal connector6232 may be turned relative to the inner and outer insulation layers6122, 6120 to sink the threaded taper 6234 into the inner and outerinsulation layers 6122, 6120 while the outer metal connector 6232 firmlycontacts the shield 6118 positioned against the inner metal connector6236. The outer metal connector 6232 may be crimped or welded into placeover the shield 6118 and the inner metal connector 6236.

FIG. 48 shows an embodiment with an additional feature that may beincluded for a joint 6276, which may be of various types such as thebutt, scarf, or lap joints 6130, 6140, and 6150. At the joint 6276, theouter metal connector 6131, 6174 of the lead 6108 encounters anotherlayer 6278. This layer 6278 may be the insulation extension 6132 and/orthe replacement outer insulation layer 6152. In either case, wires ofthe shield 6118 may partially extend into the layer 6278. However, priorto bonding the layer 6278 to the layer 6122, the ends of the wires ofthe shield 6118 may be individually folded over at areas 6274 as shownin FIG. 48. In this manner, the folded over ends are less likely to frayand migrate.

Embodiments as disclosed in relation to FIGS. 49-58 provide for rotationof a stylet within a lumen of an implantable medical lead by applyingrotation directly to the implantable medical lead. The implantablemedical lead has torsional stiffness and is rotationally coupled to thestylet. The torsional stiffness may be provided by features within thejacket of the lead body, such as a shield. The rotational coupling ofthe implantable medical lead to the stylet may be provided via featuresof the lead and/or stylet.

FIG. 49 shows a scenario where an implantable medical lead 7108 is beingimplanted within a patient. The lead 7108 enters the patient at anintroduction site 7112 where an introduction needle provides apassageway into the body. The lead 7108 is shown transparently forpurposes of illustration to reveal a stylet 7132 present within a lumenof the lead 7108. The stylet 7132, and specifically the bent tip 7134 ofthe stylet 7132, is used to steer the lead 7108 as the lead 7108 isbeing inserted in order to direct the distal end of the lead 7108 to thestimulation site which may be a significant distance from theintroduction site 7112.

The bent tip 7134 is rotated in position by the stylet 7132 beingrotated. The stylet 7132 may include a stylet hub 7130 on the proximalend. This stylet hub 7130 may engage the lead 7108 as discussed below.To rotate the stylet 7132 and the bent tip 7134, the doctor may applyrotation 7136 directly to the lead 7108 at the introduction site 7112rather than reaching back to grasp the stylet hub 7130. The lead 7108 istorsionally stiff such that the rotation 7136 causes rotation along thelength of the lead 7108 including rotation 7138 near the proximal end,rotation 7142 of the hub, and rotation 7140 near the distal end.

The stylet 7132 is rotationally coupled to the lead 7108 at one or morepoints. The rotational coupling may be near the proximal end or thedistal end of the lead 7108, and this rotational coupling may be done invarious ways as described below. Thus, the rotation 7136 being appliedto the lead 7108 at the introduction site 7112 causes the stylet 7132 torotate along the length to the bent tip 7134.

The stylet 7132 and stylet hub 7130 may be constructed of variousmaterials. For example, the stylet may be constructed of steel,stainless steel, tungsten, beryllium, and their alloys which providestorsional rigidity. The stylet hub may be constructed of variousmaterials such as nylon, polycarbonate, or other rigid engineeringplastics.

FIG. 50 shows an implantable medical system in place once the lead 7108has been directed to the stimulation site. The implantable medicalsystem includes an IMD 7102 having a biocompatible case and a header7106. The lead 7108 includes distal electrodes 7116 at the stimulationsite that are used to provide the stimulation. The lead also includesproximal connectors 7110 that are fixed by a set screw or othermechanism within the header 7106 and are connected to electricalcircuitry of the IMD 7102. The IMD 7102 produces stimulation signalsthat are provided to the connectors 7110. Filars within the lead 7108carry the stimulation signals from the connectors 7110 to the electrodes7116.

FIGS. 51 and 52 show an embodiment of the implantable medical lead 7108where a shield 7118 is present that provides the torsional rigidity. Anouter jacket layer 7120 is shown transparently in FIG. 51 for purposesof illustrating the shield 7118. The shield 7118 may be included forvarious reasons in addition to creating the torsional rigidity. Forexample, the shield 7118 may provide protection from unwanted RF energy.For instance, the lead 7108 may be a magnetic resonance imaging (MRI)safe lead that allows the patient to have an MRI scan without riskingtissue damage due to induced RF currents in the filars of the lead 7108.The conductive filars 7124 extend the length of the lead 7108 andinterconnect the proximal connectors 7110 to the distal electrodes 7116so that stimulation signals are conducted from the proximal end to thedistal end of the lead 7108.

As shown in FIG. 51, the shield 7118 of this example is a braided metalwire. The metal wire may be constructed of various materials such astitanium, tantalum, platinum, stainless steel, and their alloys, orother metals. It may be desired to utilize a biocompatible metal for theshield 7118, particularly for embodiments where a portion of the shield7118 may be exposed for purposes of grounding. While the shield 7118 isshown as a braid, other shield configurations may be chosen such as ametal foil that is wrapped in an overlapping fashion. If shielding isnot desired, then the foil may be more loosely wrapped and still providetorsional rigidity.

As shown in FIG. 52, the shield 7118 may be embedded within the jacketof the lead 7108. One manner of constructing the lead 7108 with theshield 7118 is to provide an inner jacket 7122 that encloses the filars7124 and any additional insulation layer 7126 that may surround eachfilar 7124. The shield 7118 may then reside on the outer portion of theinner jacket 7122, and the outer jacket 7120 may then enclose the shield7118.

The shield 7118 may ground to tissue via an RF coupling through theouter layer 7120 and/or via grounding to the can 7104 and/or to thetissue via ground rings. For embodiments where it is desirable for theshield 7118 to RF couple to tissue, the outer jacket layer 7120 may berelatively thin, such as on the order of 0.5 to 5 mils. Where the shield7118 grounds at the can of the IMD and grounding via a RF coupling fromthe shield 7118 through the outer jacket 7120 directly to the tissue isof less significance, then the shield 7118 may be located further fromthe outer surface of the lead 7108. The outer jacket 7120 may be addedover the shield 7118 by shrinking in place or by being extruded over theshield 7118.

The inner and outer jackets 7122, 7120 may be constructed of the same orsimilar materials such as various flexible and biocompatible polymers,examples of which are polyurethanes and silicones. The lumen 7128 isincluded in the inner jacket 7122, particularly for percutaneous leads7108, to allow the stylet 7132 to be inserted for purposes of pushingand steering the lead into the desired position within the patient.

As shown in the cross-section of FIG. 52, at this particular point alongthe lead the stylet 7132 is free within the lumen 7128. The stylet 7132has clearance relative to the lumen 7128. This clearance may aid in theinsertion of the stylet 7132 into the lumen 7128.

FIG. 53 shows a cross-section at a point along an embodiment of the lead7108 where a rotational coupling is established between the lead 7108and the stylet 7132. At this point, the lumen 7128 of the lead 7108 hasa portion forming a passageway 7144 that has a square cross-sectionalshape rather than being round. As one example, this passageway 7144 maybe created in the distal tip of the lead 7108, distal to the location ofthe distal electrodes. The stylet 7132 likewise has a shaft 7146 thathas a square cross-sectional shape and that fits within the squareshaped passageway 7144 of the lumen 7128. The position of the squareshaped passageway 7144 may be such that when the stylet 7132 is fullyinserted in the lead 7108, the square shaped shaft 7146 of the stylet7132 mates to the square shaped passageway 7144 of the lumen 7128. Thesquare shape effectively keys the stylet 7132 to the lead 7108 so that arotational coupling is achieved.

FIG. 54 shows a cross-section at a point along another embodiment of thelead 7108 where a rotational coupling is established between the lead7108 and the stylet 7132. At this point, the lumen 7128 of the lead hasa particular portion forming a passageway 7148 that has a starcross-sectional shape rather than being round. As one example, thispassageway 7148 may be created in the distal tip of the lead 7108,distal to the location of the distal electrodes. The stylet 7132likewise has a shaft 7150 that has a star cross-sectional shape and thatfits within the star shaped passageway 7148 of the lumen 7128. Theposition of the star shaped passageway 7148 may be such that when thestylet 7132 is fully inserted in the lead 7108, the star shaped shaft7150 of the stylet 7132 mates to the star shaped passageway 7148 of thelumen 7128. The star shape effectively keys the stylet 7132 to the lead7108 so that a rotational coupling is achieved.

FIG. 55 shows a cross-section at a point along another embodiment of thelead 7108 where a rotational coupling is established between the lead7108 and the stylet 7132. At this point, the lumen 7128 of the lead hasa particular portion forming a passageway 7152 that has a hexagonalcross-sectional shape rather than being round. As one example, thispassageway 7152 may be created in the distal tip of the lead 7108,distal to the location of the distal electrodes. The stylet 7132likewise has a shaft 7154 that has a hexagonal cross-sectional shape andthat fits within the hexagonal shaped passageway 7152 of the lumen 7128.The position of the hexagonal shaped passageway 7152 may be such thatwhen the stylet 7132 is fully inserted in the lead 7108, the hexagonalshaped shaft 7154 of the stylet 7132 mates to the hexagonal shapedpassageway 7152 of the lumen 7128. The hexagonal shape effectively keysthe stylet 7132 to the lead 7108 so that a rotational coupling isachieved.

The square, star, and hexagonal shapes are shown for purposes ofillustration. It will be appreciated that any number of shapedengagements may be utilized to establish a rotational coupling betweenthe lead 7108 and the stylet 7132. Furthermore, it will be appreciatedthat the coupling may occur at any point or multiple points along thelead 7108 where the torsional stiffness is present

FIG. 56 shows a side view of a proximal end of the lead 7108 with thelumen 7128 engaging an embodiment of the stylet hub 7130 in order toestablish a rotational coupling between the stylet 7132 and the lead7108. The stylet hub 7130 includes a tapered region 7156 that extendsfrom the hub 7130 to the stylet 7132. This tapered region 7156 at alarge diameter end has a diameter larger than that of the lumen 7128. Asa result, the tapered region 7156 may be press fit into the lumen 7128of the lead 7108 in order to produce a frictional fit that establishes arotational coupling.

FIG. 57 shows a side view of a proximal end of the lead 7108 with thelumen 7128 engaging another embodiment of the stylet hub 7130 in orderto establish a rotational coupling between the stylet 7132 and the lead7108. The stylet hub 7130 includes a splined region 7158 that extendsfrom the hub 7130 to the stylet 7132. The diameter created by thesplined region 7158 may be greater than the diameter of the lumen 7128.This splined region 7158 may be press fit into the lumen 7128 of thelead 7108 in order to engage the splines with the lumen 7128 toestablish a rotational coupling.

FIG. 58 shows a side view of a proximal end of the lead 7108 with thelumen 7128 engaging another embodiment of the stylet hub 7130 in orderto establish a rotational coupling between the stylet 7132 and the lead7108. The stylet hub 7130 includes a threaded region 7160 that extendsfrom the hub 7130 to the stylet 7132. The diameter created by thethreaded region 7160 may be greater than the diameter of the lumen 7128.This threaded region 7160 may be screwed into the lumen 7128 of the lead7108 in order to engage the threads with the lumen 7128 to establish arotational coupling.

The tapered, splined, and threaded engagements of the hub 7130 to thelumen 7128 are shown for purposes of illustration. It will beappreciated that any number of hub features may be used to engage thelumen 7128 to provide the rotational coupling. It will be furtherappreciated that similar features may be used to allow the hub 7130 toinstead engage the outer layer 7120 of the lead 7108 at the proximal endsuch as by having a taper, splines, or threads that surround the outerlayer 7120 but with a smaller diameter than the outer layer 7120. Thesefeatures face inward to engage the outer layer 7120 and establish therotational coupling.

Embodiments as disclosed in relation to FIGS. 59-72 provide radiopaquemarkers that are added to implantable medical leads or to implantablemedical devices (IMD) connected to the leads to identify the leads asbeing designed for safe application of a medical procedure such as anMRI scan. The radiopaque markers are visible on an X-ray or duringfluoroscopy so that administering personnel can have a visual assurancethat the lead is designed for safe application of the medical procedureof interest.

FIG. 59 shows an embodiment of an implantable medical system thatincludes an IMD 8102 having a can 8104 that houses electronics and aheader 8106. In this example, the IMD 8102 provides signals to a pair ofimplantable medical leads 8108, 8109 which are physically andelectrically connected to the IMD 8102 via the header 8106.

Radiopaque markers 8130, 8131 are provided to identify the leads 8108,8109 as being safe for a given procedure. In this particular example,the radiopaque markers 8130, 8131 are tags that are fixed directly tocorresponding leads 8108, 8109. Sutures 8132 of the permanent type holdthe tag 8130 to the lead 8108 while sutures 8133 hold the tag 8131 tothe lead 8109. By individually tagging both leads 8108, 8109, theadministering personnel can be assured that both leads are safe for thegiven procedure.

The tags 8130, 8131 may be added after the leads 8108, 8109 have beensuccessfully implanted into the patient. For percutaneous leads, this isparticularly desirable because the lead 8108, 8109 is inserted into thebody of the patient via an introducer needle that lacks clearance forthe tags 8130, 8131. Thus, once the leads 8108, 8109 are in positionwith the proximal ends of the leads being near the incision site andwith the introducer needle removed, the tags 8130, 8131 can be insertedinto a pocket made for the IMD 8102 and sutured in place by the doctor.

The tags 8130, 8131 may be constructed of a biocompatible material thathas a density that is adequately radiopaque by being visible on an X-rayor during fluoroscopy. Examples of such materials include barium,tantalum, platinum, and platinum-iridium. The size of the tags 8130,8131 may vary but when sized to have a length and width in the range of0.25 to 5 centimeters and 0.01 to 0.2 inch thickness, the tag 8130, 8131is adequately visible while being small enough to comfortably fit withinor nearby the pocket near the IMD 8102.

When administering personnel wish to perform a given medical proceduresuch as an MRI, the personnel may take an X-ray or conduct fluoroscopyto look for the radiopaque marker. The IMD 8102 itself may need to alsobe designed for safety during a given medical procedure and may have itsown internal or external radiopaque marker. Thus, placing the tags 8130,8131 nearby the IMD 8102 may be desirable so that the tags of both theleads 8108, 8109 and the marker of the IMD 8102 are in the same field ofview of an X-ray or during fluoroscopy.

In this example of FIG. 59, the tags 8130, 8131 include an aperture8138, 8139 in the shape of a particular symbol. Due to the aperture8138, 8139, this shape within the tag 8130, 8131 is visiblydistinguishable on the X-ray or during fluoroscopy. Thus, this aperture8138, 8139 may identify the safety aspects of the lead 8108, 8109 and/orthe medical procedures that are safe to conduct. The shape of theapertures 8138, 8139 in FIG. 59 is a wave that represents that the leads8108, 8109 are safe for an MRI scan conducted within normal operatingparameters.

FIG. 60 shows a similar configuration for the radiopaque tag 8130.However, rather than the doctor suturing the tag 8130 to the lead 8108,the doctor connects the proximal end of the lead 8108 to the IMD 8102that is placed into the pocket and sutures the tag 8130 to the IMD 8102.In the example shown, sutures 8132 extending from the tag 8130 are tiedaround the can 8104. It will be appreciated that the sutures 8132 couldbe tied to the IMD 8102 in other ways or to designated features of theIMD 8102.

FIG. 61 shows another example of placing the tag 8130 in close proximityto the IMD 8102 and lead 8108. However, in this example, the tag 8130 isnot tied to either but is instead left loosely positioned within thepocket 8136 where the IMD 8102 is positioned. The pocket 8136 preventsthe tag 8130 from migrating away from the position of the IMD 8102 sothat the tag 8130 remains in the same field of view as the IMD 8102 andlead 8108 during an X-ray or fluoroscopy.

FIG. 62 shows another example of placing the tag 8130 in close proximityto the IMD 8102 and the lead 8108. In this example, rather than suturingthe tag 8130 to the lead 8108, the doctor may have chosen to bond thetag 8130 to the lead using a glue 8140. Examples of a glue suitable forbonding the tag 8130 to the lead 8108 include medical adhesives.

FIG. 63 shows another example of placing the tag 8130 in directproximity of the IMD 8102 by bonding the tag 8130 to the IMD 8102. Here,the tag 8130 is bonded to the IMD 8102 with the glue 8140. Examples of aglue suitable for bonding the tag 8130 to the IMD 8102 also includemedical adhesives.

FIG. 64 shows another example of placing the tag 8130 in close proximityto the IMD 8102 and the lead 8108. In this example, the tag 8130 isattached to a clamp 8142, such as a U-shaped spring-loaded clamp orother clamp structures such as features that mechanically lock includingdetents. The clamp 8142 tightens against the lead 8108 to hold the tag8130 in position relative to the lead 8108.

FIG. 65 shows another example of placing the tag 8130 in directproximity to the IMD 8102. Here, the tag 8130 includes the clamp 8142which is tightened against the can 8104 of the IMD 8102. The clamp 8142could tighten against other portions of the IMD 8102 as well such as theheader 8106. The clamp 8142 of FIG. 65 may be of the same typesdiscussed above in relation to FIG. 64.

FIG. 66 shows another example of placing the tag 8130 in close proximityto the IMD 8102 and the lead 8108. In this example, the tag 8130 has anextension 8144 that forms a ring shape. Initially, the extension 8144may be an open ring so that it easily fits onto the lead 8108. Theextension 8144 may then be crimped to form a closed or nearly closedring about the lead 8108 and to fix the tag 8130 relative to the lead8108.

FIG. 67A shows an example of a radiopaque marker being installed on alead where the radiopaque marker is not a tag. Instead, the radiopaquemarker is a radiopaque coil 8146′ that is in a radially expanded stateproduced by axially compressing the coil 8146′. The radially expandedstate allows the coil 8146′ to be placed about the lead 8108, with thelead 8108 traveling through the center of the coil in an axialdirection. The coil 8146′ is placed onto the proximal end of the lead8108, shown here with connectors 8110, prior to the proximal end beinginserted into the header 8106.

FIG. 67B shows the radiopaque coil 8146 in a radially contracted state.Here, once properly positioned along the lead 8108, the coil 8146 hasbeen allowed to naturally expand axially to radially contract until thecoil diameter meets that of the lead 8108 to fix the coil 8146 in placeon the lead 8108. The lead 8108 is then connected to the IMD 8102, withthe coil 8146 being located in proximity to the IMD 8102 in this exampleso as to be in the same field of view. The coil 8146 itself is thevisible shape that indicates that the lead 8108 is safe for a particularmedical procedure such as an MRI.

The radiopaque coil 8146 may be constructed of materials similar to thetag 8130. For instance, the coil 8146 may be constructed of barium,tantalum, platinum, and platinum-iridium. The size of the coil 8146 mayvary but when sized in the range of 0.04 inch to 1.0 inch in length andfrom 2 mils to 0.10 inch in diameter when radially contracted, the coil8146 is adequately visible while being small enough to comfortably fitwithin or nearby the pocket near the IMD 8102.

FIGS. 68A and 68B show an example of a tool 8150 being used to place thecoil 8146′ in the radially expanded state onto the lead 8108 and todeposit the coil 8146 in the radially contracted state at the desiredposition on the lead 8108. The tool 8150 holds the coil 8146′ in theradially expanded state by providing a larger diameter than the lead8108 and while providing a passageway for the lead 8108.

As shown in FIG. 68B, the tool 8150 is positioned on the lead 8108 withthe lead 8108 passing through the passageway of the tool 8150. The coil8146′ is pushed off of the tool 8150 until the coil 8146 has a radiallycontracted end about the lead 8108. The tool 8150 may then be pulledaway from the lead 8108 to allow the remainder of the coil 8146′ in theradially expanded state to slide off of the tool 8150 and onto the lead8108 where the coil 8146 achieves the radially contracted state.

FIG. 69A shows a polymer structure 8152 that may be used to place aradiopaque marker onto the lead 8108. FIG. 69B shows the polymerstructure 8152 once positioned on the lead 8108. This polymer structure8152 includes a cylindrical aperture 8154 that allows the lead 8108 topass through. The cylindrical aperture 8154 may stretch to a largerdiameter than the lead 8108 such as by using a conventional anchordeployment tool to position the polymer structure onto the lead 8108.The polymer structure 8152 may then be removed from the anchor tool toallow the polymer structure 8152 to contract onto the lead 8108.

The polymer structure 8152 includes an offset portion 8155. Within thisoffset portion 8155, a radiopaque plate 8156 is embedded. The radiopaqueplate 8156 may include a symbol 8158 or other information to be conveyedto administering personnel. The radiopaque plate 8156 may be constructedof materials similar to the tag 8130. For instance, the plate 8156 maybe constructed of barium, tantalum, platinum, and platinum-iridium. Thesize of the plate 8156 may vary but when sized in at about 0.040 inch inlength/width and about 0.01 to 0.2 inch thick, the plate 8156 isadequately visible while being small enough to be contained within thepolymer structure 8152.

The polymer structure 8152 of FIGS. 69A and 69B is similar to a leadanchor. However, this polymer structure 8152 lacks suture wings. Becausethe contraction of the cylindrical aperture 8154 holds the polymerstructure in place, no sutures are needed.

The offset of the portion 8155 where the radiopaque plate 8156 islocated provides for ease of removal of the polymer structure 8152 fromthe lead 8108. An axial cut can be made along the cylindrical aperture8154 because the radiopaque marker does not surround the cylindricalaperture 8154. However, if ease of removal is not of concern, thenembodiments may provide the radiopaque plate 8156 centered about thecylindrical aperture 8154.

FIG. 69C shows a similar polymer structure 8168. However, the polymerstructure 8168 is in the form of a lead anchor that includes suturewings 8170 while also including the radiopaque plate 8156. Rather thanrelying on the cylindrical aperture to contract onto the lead 8108, thelead anchor 8168 may additionally or alternatively have sutures 8132that tie the suture wings 8170 to the lead 8108 to hold the polymerstructure 8168 in place in proximity to the IMD 8102. The radiopaqueplate 8156 may be centered about the lead 8108 within the polymerstructure 8160 even where ease of removal is desired if the polymerstructure 8160 is held in place by the sutures 8132 rather than acontracted state upon the lead 8108.

FIG. 70A shows another polymer structure 8160 that may be used to placea radiopaque marker onto the lead 8108. FIG. 70B shows the polymerstructure 8160 once positioned on the lead 8108. This polymer structure8160 includes a cylindrical aperture 8162 that allows the lead 8108 topass through. The cylindrical aperture 8162 may stretch to a largerdiameter than the lead 8108 such as by using a conventional anchordeployment tool to position the polymer structure 8160 onto the lead8108. The polymer structure 8160 may then be removed from the anchortool to allow the polymer structure 8160 to contract onto the lead 8108.

The polymer structure 8160 includes an offset portion 8164. Within thisoffset portion 8164, a radiopaque coil 8166 is embedded. The radiopaquecoil 8166 may form a symbol or other information to be conveyed toadministering personnel. The radiopaque coil 8166 may be constructed ofmaterials similar to the coil 8146. For instance, the coil 8166 may beconstructed of barium, tantalum, platinum, and platinum-iridium. Thesize of the coil 8166 may vary but when sized in the range of 0.04 to1.0 inch in length and 2 mils to 0.10 inch in wire diameter with anoverall diameter of 0.020 to 0.5 inch, the coil 8166 is adequatelyvisible while being small enough to be contained within the polymerstructure 8160.

The polymer structure 8160 of FIGS. 70A and 70B is also similar to alead anchor. However, this polymer structure 8160 lacks suture wings.Because the contraction of the cylindrical aperture 8162 holds thepolymer structure 8160 in place, no sutures are needed.

The offset of the portion 8164 where the radiopaque coil 8166 is locatedprovides for ease of removal of the polymer structure 8160 from the lead8108. An axial cut can be made along the cylindrical aperture 8162because the radiopaque marker does not surround the cylindrical aperture8162. However, if ease of removal is not of concern, then embodimentsmay provide the radiopaque coil 8166 centered about the cylindricalaperture 8162.

FIG. 70C shows a similar polymer structure 8172. However, the polymerstructure 8172 is in the form of a lead anchor that includes suturewings 8174 while also including the radiopaque coil 8166. Rather thanrelying on the cylindrical aperture to contract onto the lead 8108, thelead anchor 8172 may additionally or alternatively have sutures 8132that tie the suture wings 8174 to the lead 8108 to hold the polymerstructure 8172 in place in proximity to the IMD 8102. The radiopaquecoil 8166 may be centered about the lead within the polymer structure8172 even where ease of removal is desired if the polymer structure 8172is held in place by the sutures 8132 rather than a contracted state uponthe lead 8108.

FIGS. 71 and 72 show an embodiment of the implantable medical lead 8108where a shield 8118 is present. This shield 8118 may provide protectionfrom RF energy that allows the lead 8108 to be conditionally MRI safeand thus eligible to carry the radiopaque marker for an MRI. An outerjacket layer 8120 is shown transparently in FIG. 71 for purposes ofillustrating the shield 8118. The shield 8118 may provide protectionfrom RF energy of an MRI that might otherwise cause tissue damage due toinduced RF currents in the filars of the lead 8108. The conductivefilars 8124 extend the length of the lead 8108 and interconnect theproximal connectors 8110 to the distal electrodes so that stimulationsignals are conducted from the proximal end to the distal end of thelead 8108.

As shown in FIG. 71, the shield 8118 of this example is a braided metalwire. The metal wire may be constructed of various materials such astitanium, tantalum, niobium, platinum-iridium alloy, platinum,palladium, gold, stainless steel, and their alloys, or other metals. Itmay be desired to utilize a biocompatible metal for the shield 8118,particularly for embodiments where a portion of the shield 8118 may beexposed for purposes of grounding. While the shield 8118 is shown as abraid, other shield configurations may be chosen particularly whereflexibility is not an issue such as a foil strip wrapped about the lead8108 in an overlapping manner or an outer layer 8120 that is heavilydoped with conductive particles.

As shown in FIG. 72, the shield 8118 may be embedded within the jacketof the lead 8108. One manner of constructing the lead 8108 with theshield 8118 is to provide an inner jacket 8122 that encloses the filars8124 and any additional insulation layer 8126 that may surround eachfilar 8124. The shield 8118 may then reside on the outer portion of theinner jacket 8122, and the outer jacket 8120 may then enclose the shield8118.

The shield 8118 may ground to tissue via an RF coupling through theouter layer 8120 and/or via grounding to the can 8104 and/or to thetissue via ground rings. For embodiments where it is desirable for theshield 8118 to RF couple to tissue, the outer jacket layer 8120 may berelatively thin, such as on the order of 0.5 to 5 mils. Where the shield8118 grounds at the can 8104 of the IMD 8102 and grounding via a RFcoupling from the shield 8118 through the outer jacket 8120 directly tothe tissue is of less significance, then the shield 8118 may be locatedfurther from the outer surface of the lead 8108. The outer jacket 8120may be added over the shield 8118 by shrinking in place or by beingextruded over the shield 8118.

The inner and outer jackets 8122, 8120 may be constructed of the same orsimilar materials such as various flexible and biocompatible polymers,examples of which are polyurethanes and silicones. A lumen 8128 may beincluded inside of the inner jacket 8122 around which the insulatedfilars 8124 are coiled or otherwise positioned. The lumen 8128 may beuseful, particularly for percutaneous leads 8108, to allow a stylet tobe inserted for purposes of pushing and steering the lead 8108 into thedesired position within the patient.

Embodiments as disclosed in relation to FIGS. 73-76D provide for reducedtorsional stiffness of a shield present within an implantable medicallead for use with an implantable medical device (IMD). The torsionalstiffness of the shield may be reduced in various ways such as byaxially cutting the shield to form a slot that breaks thecircumferential mechanical continuity of the shield. The slot may thenbe closed to re-establish the circumferential shielding continuity ofthe shield and to preserve the shielding function.

FIG. 73 shows an example of an implantable medical system 9100 thatincludes an IMD 9102 coupled to a lead 9108. The IMD 9102 includes ametal can 9104, typically constructed of a medical grade titanium, suchas grades 1-4, 5 or 9 titanium, or similar other biocompatiblematerials. The IMD 9102 includes a header 9106 typically constructed ofmaterials such as polysulfone or polyurethane, that is affixed to themetal can 9104. The header 9106 is shown transparently for purposes ofillustration. The header 9106 provides a structure for securing the lead9108 to the IMD 9102 and for establishing electrical connectivitybetween circuitry of the IMD 9102 and electrodes of the lead 9108.

The lead 9108 includes electrodes 9116 on a distal end that arepositioned at a stimulation site within a patient. The lead alsoincludes connector rings 9110 on a proximal end that is positionedwithin the header 9106. The connector rings 9110 make physical contactwith electrical connections 9111 within the header. The electricalconnections 9111 may include a metal contact that the connector ring9110 rests against upon being inserted into the header 9106 where a wireextends from the metal contact into the can 9104 where the circuitry ishoused. Signals applied by the IMD 9102 to the connector rings 9110 areconducted through the lead 9108 to the electrodes 9116 to provide thestimulation therapy to the patient.

The lead 9108 is secured in the header 9106 such as by a set screw block9112 within the header 9106 that allows at least one set screw 9114 tobe tightened against at least one of the connector rings 9110. A shield9118 as shown in FIGS. 74A and 74B may be grounded to the body along oneor more points down the length of the lead from the IMD 9102 viacapacitive coupling through the jacket or via ground rings. The shield9118 may also be grounded at the can 9104 of the IMD 9102 of FIG. 73.

FIGS. 74A and 75A show an example of the lead 9108, where a shield 9118is present. An outer insulation layer 9120 of a lead jacket is showntransparently in FIG. 74A for purposes of illustrating the shield 9118.The shield 9118 blocks at least some RF energy from directly coupling toconductive filars 9124 that are present within the lead 9108. Theconductive filars 9124 extend the length of the lead and interconnectthe proximal connector rings 9110 to the distal electrodes 9116 so thatstimulation signals are conducted from the proximal end to the distalend of the lead 9108.

As shown in FIG. 74A, the shield 9118 of this example is a braidedcollection of metal wires. The metal wires may be constructed of variousmaterials such as titanium, tantalum, niobium, platinum-iridium alloy,platinum, palladium, gold, stainless steel, and their alloys, or othermetals. It may be desired to utilize a biocompatible metal for theshield 9118, particularly for embodiments where a portion of the shield9118 may be exposed for purposes of grounding. While the shield 9118 isshown as a braid, other shield configurations may be chosen particularlywhere flexibility is not an issue such as a coiled configuration, foilstrip wrapped about the lead 9108 in an overlapping manner or an outerlayer 9120 that is heavily doped with conductive particles.

As shown in FIG. 75A, the shield 9118 may be embedded within the jacketof the lead 9108. One manner of constructing the lead 9108 with theshield 9118 is to provide an inner insulation layer 9122 of the jacketthat encloses the filars 9124 and any additional insulation layer 9126,such as polytetrafluoroethylene (PTFE) that may surround each filar9124. The shield 9118 may then reside on the outer portion of the innerinsulation layer 9122, and the outer insulation layer 9120 may thenenclose the shield 9118. The outer insulation layer 9120 may be addedover the shield 9118 and shrunk in place or may be extruded over theshield 9118. The outer jacket 9120 maybe added over the braid 9118, orit may be extruded over the braid.

For embodiments where it is desirable for the shield 9118 to RF coupleto tissue, typically as a capacitive coupling, in addition to groundingat the can 9104 or along the lead 9108, the amount of the outer jacketlayer 9120 covering the shield 9118 may be relatively thin, such as onthe order of 0.5 to 5 mils. Where the shield 9118 grounds at one or morespecific locations along its length, via a direct current coupling or acapacitive coupling, the shield 9118 may be located further from theouter surface of the lead 9108.

The inner and outer insulation layers 9122, 9120 of the jacket may beconstructed of the same or similar materials such as various flexibleand biocompatible polymers, examples of which are polyurethanes andsilicones. A lumen 9128 may be included inside of the inner jacket 9122around which the insulated filars 9124 are coiled or otherwisepositioned. The lumen 9128 may be useful, particularly for percutaneousleads 9108, to allow a stylet to be inserted for purposes of pushing andsteering the lead 9108 into the desired position within the patient.

As shown, the shield 9118 has mechanical and shielding continuity aboutthe circumference of the inner insulation layer 9122. This continuity isachieved by the wires of the braided shield 9118 being continuous. Thecircumferential shielding continuity exists because there are nonon-conductive openings large enough to allow RF energy to easily passthrough. The mechanical continuity produces a large increase intorsional stiffness over an unshielded lead, which may be beneficial insome respects but is detrimental in other respects.

The detrimental aspects may include difficulties twisting the leadduring implant procedures due to high torsional stiffness. Twisting thelead 9108 may be beneficial when guiding the lead 9108 to thestimulation site and to the IMD 9102 and when wrapping excess lengths ofthe lead 9108 about the IMD 9102. Thus, in some instances, it may bedesirable to provide a shielded implantable medical lead with reducedtorsional stiffness.

FIGS. 74B and 75B show the lead 9108 once the shield 9118 has been cutin an axial direction to create a slot 9140. A shield portion 9142creates one edge of the slot 9140 while an opposing shield portion 9144creates the opposite edge. The slot 9140 may be created by a single cutor by two cuts that are roughly parallel and result in a section of theshield 9118 being removed. The shield 9118 may be cut prior to applyingthe outer layer 9120 so that the outer layer 9120 does not need to becut to cut the shield 9118.

The shield 9118 of FIG. 74B now lacks the circumferential mechanicalcontinuity due to the slot 9140, and the torsional stiffness is reducedconsiderably as a result. However, the slot 9140 also breaks thecircumferential shielding continuity because the slot 9140 has an axialdimension that allows RF energy to easily pass through the slot 9140.Therefore, to preserve the RF shielding function of the shield 9118, theslot 9140 is closed in one of various ways that re-establishes thecircumferential shielding continuity while allowing the circumferentialmechanical continuity to remain broken.

FIGS. 74C and 75C show one embodiment of the lead 9108 where the slot9140 is closed to re-establish circumferential shielding continuity byclosing the slot sufficiently relative to the wavelengths of RF energyso that the RF energy cannot easily penetrate the shield 9118 at thelocation of the slot 9140. In this example, the shield portion 9144 lapsover the shield portion 9142 to close the slot 9140 from a shieldingcontinuity standpoint. The shield portion 9144 may or may not contactthe shield portion 9142 such that circumferential electrical continuitymay or may not be re-established. However, either way, the shieldportion 9144 is not bonded to the shield portion 9142 such that theyremain mobile with respect to one another, thereby maintaining the breakin the circumferential mechanical continuity.

The shield portion 9144 may be lapped onto the shield portion 9142 as anatural result of cutting the shield 9118, such as where the shield 9118is loosely braided over the inner insulation layer 9122. The loosebraiding provides an uncut shield diameter that is slightly larger thanthe diameter of the inner insulation layer 9122 such that cutting theshield 9118 to create the slot 9140 allows the shield portion 9144 tocollapse onto the shield portion 9142. This collapse of the shield 9118closes the slot 9140 while the shield diameter is reduced down to thediameter of the inner insulation layer 9122.

The outer insulation layer 9120 is then added over the shield 9118. Theouter insulation layer 9120 is a polymer that holds the shield 9118 inplace against the inner insulation layer 9122. However, the polymer ofthe outer insulation layer 9120 is compliant so that the shield portion9144 can move relative to the shield portion 9142 upon application oftorque to the lead 9108.

FIGS. 74D and 75D show another embodiment of the lead 9108 where theslot 9140 is closed to re-establish circumferential shielding continuityby closing the slot 9140 sufficiently relative to the wavelengths of RFenergy so that the RF energy cannot easily penetrate the shield 9118 atthe location of the slot 9140. In this example, the slot 9140 is closedby application of a shield patch 9146. The shield patch 9146 may beconstructed similarly to the braided shield 9118, using the same orsimilar metal wire. In the example shown, the shield patch 9146 is agrid pattern, but it will be appreciated that other patterns may also beused such as where the grid includes U-shaped portions along the axialwires so that the U-shaped portions allow for axial extension of thelead 9108. The shield patch 9146 overlaps onto the shield 9118 on bothsides of the slot 9140. The shield portion 9144 may or may not contactthe shield portion 9142 such that circumferential electrical continuitymay or may not be re-established. However, either way, the shield patch9146 is not bonded to the shield 9118 such that the shield patch 9146can move relative to the shield 9118 on either side of the slot 9140. Asa result, the circumferential mechanical continuity of the shield 9118remains broken.

Because the shield patch 9146 is being added to the lead 9108, thebraided shield 9118 may be applied to the inner insulation layer 9122 ina close fitting manner as opposed to loosely braiding the shield 9118.Once the cut is complete, the shield patch 9146 may then be placed intoposition directly onto the shield 9118 and across the slot 9140.

The outer insulation layer 9120 is then added over the shield 9118 andthe shield patch 9146. As in the embodiment of FIGS. 74C and 75C, theouter insulation layer 9120 is a polymer, and the outer insulation 9120holds the shield 9118 in place against or close to the inner insulationlayer 9122 and also holds the shield patch 9146 in place against orclose to the shield 9118. However, the polymer of the outer insulationlayer 9120 is compliant so that the shield patch 9146 can move relativeto the shield 9118 on either or both sides of the slot 9140 uponapplication of an axial twisting moment to the lead 9108.

FIG. 76A shows a representation of a shield 9150 that may be used in animplantable medical lead 9108. The representation is a tube, and thistube is illustrative for multiple reasons. Where the shield 9150 is abraided shield, such as the shield 9118, the apertures are smallrelative to the wavelengths of the RF energy such that the braidedshield 9118 is effectively a tube from the perspective of the RF energy.Where the shield 9150 is another configuration, such as a foil stripwrapped around the inner insulation layer 9122 in an overlappingfashion, the foil strip forms a true tube. In either case, a linearaxial cut in the shield 9150 reduces torsional stiffness but appears asthe slot 9152, which presents an opening that the RF energy may passthrough.

FIG. 76B shows a tubular representation of the shield 9150 that maycorrespond to a braided shield or other shield configuration such as anoverlapping wrapped foil strip. Here, the shield 9150 uses the overlaptechnique such as that shown above in FIGS. 74C and 75C to close theslot 9152 formed by the linear axial cut. As can be seen, a shieldportion 9156 on one side of the slot 9152 overlaps another shieldportion 9154 on the opposite side of the slot 9152 and may or may notcontact the shield portion 9154. Thus, the slot 9152 is effectivelyclosed to establish shielding continuity across the slot 9152, but theshield portions 9154, 9156 may move relative to one another so that themechanical continuity remains broken.

FIG. 76C shows a tubular representation of the shield 9150 that may alsocorrespond to a braided shield or other shield configuration such as anoverlapping wrapped foil strip. Here, the shield 9150 uses a shieldpatch technique such as that shown above in FIGS. 74D and 75D to closethe slot 9152 formed by the linear axial cut. As can be seen, a shieldpatch 9158 reaches across the slot 9152 to overlap and may or may notphysically contact the shield 9150 on both sides of the slot 9152. Thus,the slot 9152 is effectively closed to establish shielding continuityacross the slot 9152, but the shield patch 9158 may move relative to theshield 9150 on either or both sides of the slot 9152 so that themechanical continuity remains broken.

FIG. 76D shows a tubular representation of the shield 9160 that maycorrespond to a braided shield or other shield configuration such as anoverlapping wrapped foil strip. Here, the shield 9160 has been cutaxially using a helical cut rather than a linear cut to create a helicalslot 9162. The slot 9162 breaks the circumferential mechanicalcontinuity so as to reduce the torsional stiffness, but the slot 9162also breaks the circumferential shielding continuity.

The slot 9162 may be closed using techniques discussed above. A shieldpatch may be wrapped around the helical slot 9162 to reach across theslot 9162 and achieve circumferential shielding continuity. Or, theshield 9160 may be given a larger diameter than the inner insulationlayer upon which it is positioned so that upon creating the slot 9162,the shield 9160 may collapse to create an overlap along the helical slot9162 to establish circumferential shielding continuity. This shieldpatch may be another piece of foil or may be a braided patch.

Embodiments as disclosed in relation to FIGS. 77-80C provide forguarding a termination of a shield to reduce coupling of RF energy fromthe termination of the shield to filars present within an implantablemedical lead for use with an implantable medical device (IMD). Theguarding of the termination of the shield may be done in various wayssuch as by inverting the shield near the termination such that a firstportion of the shield separates the termination of the shield from innerlayers of the lead. Other examples may involve including separate piecesof the shield to form first and second portions, where one portionseparates the termination of the other portion from the inner layers ofthe lead.

FIG. 77 shows an example of an implantable medical system 10100 thatincludes an IMD 10102 coupled to a lead 10108. The IMD 10102 includes ametal can 10104, typically constructed of a medical grade titanium, suchas grades 1-4, 5 or 9 titanium, or similar other biocompatiblematerials. The IMD 10102 includes a header 10106 typically constructedof materials such as polysulfone or polyurethane, that is affixed to themetal can 10104. The header 10106 is shown transparently for purposes ofillustration. The header 10106 provides a structure for securing thelead 10108 to the IMD 10102 and for establishing electrical connectivitybetween circuitry of the IMD 10102 and electrodes of the lead 10108.

The lead 10108 includes electrodes 10116 on a distal end that arepositioned at a stimulation site within a patient. The lead 10108 alsoincludes connector rings 10110 on a proximal end that is positionedwithin the header 10106. The connector rings 10110 make physical contactwith electrical connections 10111 within the header. The electricalconnections 10111 may include a metal contact that the connector ring10110 rests against upon being inserted into the header 10106 where awire extends from the metal contact into the can 10104 where thecircuitry is housed. Signals applied by the IMD 10102 to the connectorrings 10110 are conducted through the lead 10108 to the electrodes 10116to provide the stimulation therapy to the patient.

The lead 10108 is secured in the header 10106 such as by a set screwblock 10112 within the header 10106 that allows at least one set screw10114 to be tightened against at least one of the connector rings 10110.A shield 10118 as shown in FIGS. 78A and 78B may be grounded to the bodyalong one or more points down the length of the lead from the IMD 10102via capacitive coupling through the jacket or via ground rings. Theshield 10118 may also be grounded at the can 10104 of the IMD 10102 ofFIG. 77.

FIGS. 78A and 78B show an example of the lead 10108, where a shield10118 is present. An outer insulation layer 10120 of a lead jacket isshown transparently in FIG. 78A for purposes of illustrating the shield10118. The shield 10118 blocks at least some RF energy from directlycoupling to conductive filars 10124 that are present within the lead10108. The conductive filars 10124 extend the length of the lead andinterconnect the proximal connectors 10110 to the distal electrodes10116 so that stimulation signals are conducted from the proximal end tothe distal end of the lead 10108.

As shown in FIG. 78A, the shield 10118 of this example is a braidedcollection of metal wires. The metal wires may be constructed of variousmaterials such as titanium, tantalum, niobium, platinum-iridium alloy,platinum, palladium, gold, stainless steel, and their alloys, or othermetals. It may be desired to utilize a biocompatible metal for theshield 10118, particularly for embodiments where a portion of the shield10118 may be exposed for purposes of grounding. While the shield 10118is shown as a braid, other shield configurations may be chosenparticularly where flexibility is not an issue such as a foil stripwrapped about the lead 10108 in an overlapping manner.

FIG. 78B is a cross-section that shows one example of construction ofthe lead 10108. In this embodiment, either the guard is not provided orthe guard is not present at the area where the cross-section is taken.Thus, FIG. 78B shows the general construction of the lead 10108 withoutthe specifics of the guard which are discussed below in relation toFIGS. 79A-79C and 80A-80C. The shield 10118 may be embedded within thejacket of the lead 10108. One manner of constructing the lead 10108 withthe shield 10118 is to provide an inner insulation layer 10122 of thejacket that encloses the filars 10124 and any additional insulationlayer 10126, such as polytetrafluoroethylene (PTFE) that may surroundeach filar 10124. The shield 10118 may then reside on the outer portionof the inner insulation layer 10122, and the outer insulation layer10120 may then enclose the shield 10118. The outer insulation layer10120 may be added over the shield 10118 and shrunk in place or may beextruded over the shield 10118.

For embodiments where it is desirable for the shield 10118 to RF coupleto tissue along, typically as a capacitive coupling, in addition togrounding at the can 10104 or along the lead 10108, the entire outerjacket layer 10120 may be relatively thin, such as on the order of 0.5to 5 mils. Where the shield 10118 grounds at one or more specificlocations along its length, via a direct current coupling or acapacitive coupling, the shield 10118 may be located further from theouter surface of the lead 10108.

The inner and outer insulation layers 10122, 10120 of the jacket may beconstructed of the same or similar materials such as various flexibleand biocompatible polymers, examples of which are polyurethanes andsilicones. A lumen 10128 may be included inside of the inner jacket10122 around which the insulated filars 10124 are coiled or otherwisepositioned. The lumen 10128 may be useful, particularly for percutaneousleads 10108, to allow a stylet to be inserted for purposes of pushingand steering the lead 10108 into the desired position within thepatient.

FIG. 79A shows an embodiment of the implantable medical lead 10108 in anaxial cross-section where termination of the shield 10118 is guarded toreduce coupling of RF energy to one or more filars 10124. FIG. 80A showsa radial cross-section of the same embodiment, with the cross sectiontaken where the shield terminates. A single coiled filar 10124 is shownin this example but additional filars may be included and the filars maybe of other forms such as linear cables rather than coils. In thisexample, the shield 10118 is one continuous shield of braided metalwires, but it will be appreciated that other shields may also be usedsuch as the wrapped foil discussed above.

The shield 10118 of this example has an inversion 10136 near the distalend of the lead 10108. This inversion 10136 creates two sections to theshield 10118, a first portion 10119 that extends from the inversion10136 back to the proximal end of the lead 10108 and a second portion10121 that forms the distal termination of the shield 10118. Theinversion 10136 creates a guard for the shield termination.

The second portion 10121 is separated from the inner insulation layer10122 as well as the filars 10124 by the first portion 10119. The firstportion 10119 is braided upon the inner insulation layer 10122 and thenmay be coated with the outer insulation layer 10120 with the secondportion 10121 remaining uncoated. The inversion 10136 may then becreated so that the second portion 10121 then laps onto the outerinsulation layer 10120 so as to be separated from contact with the firstportion 10119. The second portion 10121 may extend from the inversion10136 toward the proximal end by various distances, for instance rangingfrom about ⅛ inch to about 1 inch, such that the second portion 10121may be axially shorter than the first portion 10119 which extends to theproximal end or the second portion 10121 may also extend to the proximalend. The second portion 10121 may then be covered by an additional outerinsulation layer 10117, made of the same or similar material as theouter insulation layer 10120, if it is desired that the second portion10121 be physically isolated from the body tissue.

The thickness of the outer insulation layer 10120 at the inversion 10136dictates the bend radius of the inversion 10136 where the second portion10121 laps onto the outer insulation layer 10120. It may be desirable tohave a bend radius that is sufficiently large, such as 0.002 inches, sothat the inversion 10136 does not act as a shield termination from whichRF might couple to the filars 10124. The lead diameter that is allowablefor a given application may dictate the relative thicknesses of each ofthe layers and thus set an upper limit for the bend radius of theinversion 10136.

Prior to or contemporaneously with the addition of the outer insulationlayer 10117, an extension 10132 to the outer insulation layer 10120 maybe created to extend further toward the distal end where electrodes suchas electrode 10130 are located. The extension 10132 may be constructedof the same or similar materials as that of the outer insulation layers10117, 10120. The electrode 10130 has a filar jumper wire 10134 or thefilar 10124 itself that extends through this extension 10132 and betweenthe electrode 10130 and the filar 10124. Alternatively, the area whereextension 10132 is shown may be created as a continuation of the outerinsulation layer 10117.

FIG. 79B shows another embodiment of the implantable medical lead 10108in an axial cross-section where termination of the shield 10118 isguarded to reduce coupling of RF energy to one or more filars 10124.FIG. 80B shows a radial cross-section of the same embodiment, with thecross section taken where the shield 10118 terminates. A quad coiledfilar 10124 is shown in this example but additional or fewer filars maybe included and the filars may be linear cables rather than coils. Inthis example, the shield 10118 is two separate pieces forming a firstportion 10123 and a second portion 10125 of the shield 10118 made ofbraided metal wires. It will be appreciated that either or both piecesmay be another form of a shield such as wrapped foil as discussed above.

The shield 10118 of this example has the first portion 10123 that is aseparate piece that resides at the distal end of the lead 10108 and mayextend toward the proximal end for a relatively short distance, forinstance, in the range of about ⅛ inch to about 1 inch. The firstportion 10123 is wrapped around the inner insulation layer 10122. Anintervening layer of insulation 10115 then surrounds the first portion10123.

The second portion 10125 of the shield 10118 is wrapped around theintervening layer of insulation 10115 and is therefore physicallyisolated from contact with the first portion 10123. The second portion10125 then extends on to the proximal end of the lead 10108 and maytherefore be axially longer than the first portion 10123. The outerinsulation layer 10120 then surrounds the second portion 10125. As aresult of this configuration, the first portion 10123 is located betweenthe termination point at the second portion 10125 and the inner layersincluding the inner insulation layer 10122 and filars 10124.

Because there is no inversion in this embodiment of FIGS. 79B and 80B,the thickness of the layers 10115, 10120 may not be as large as thethickness of the outer insulation layer 10120 of the embodiment of FIGS.79A and 80A where that thickness established the bend radius at theinversion 10136. As a result, the separation between the first portion10123 and the second portion 10125 may be smaller than the separationbetween the first portion 10119 and the second portion 10121 of FIGS.79A and 80A. For instance, the intervening insulation layer 10115 mayhave a thickness ranging from about 0.002 inches to about 0.006 inchesto control the separation between the first portion 10123 and secondportion 10125.

The outer insulation layer 10120 may be continued to extend on towardthe distal end of the lead 10108, including filling the area where theelectrode 10130 is located. Alternatively, prior to or contemporaneouslywith the addition of the outer insulation layer 10120, an extensionlayer from the outer insulation layer 10120 may be created to extendfurther toward the distal end where electrodes such as electrode 10130are located. The extension may be constructed of the same or similarmaterials as that of the outer insulation layers 10117, 10120.

FIG. 79C shows another embodiment of the implantable medical lead 10108in an axial cross-section where termination of the shield 10118 isguarded to reduce coupling of RF energy to one or more filars 10124.FIG. 80C shows a radial cross-section of the same embodiment, with thecross section taken where the shield 10118 terminates. A quad coiledfilar 10124 is shown in this example but additional filars may beincluded and the filars may be other forms such as linear cables ratherthan coils. In this example, the shield 10118 is two separate piecesforming a first portion 10140 and a second portion 10142 of the shield10118 made of braided metal wires, but it will be appreciated thateither piece may be another form of a shield such as wrapped foil asdiscussed above.

The shield 10118 of this example has the first portion 10140 that is aseparate piece that resides at the distal end of the lead 10108 and thathas an inversion 10138 to establish a first sub-portion 10146 and asecond sub-portion 10144. Both sub-portions 10144, 10146 may extendtoward the proximal end of the lead 10108 for a relatively shortdistance in the range of about ⅛ inch to about 1 inch. The firstsub-portion 10146 is wrapped around the inner insulation layer 10122. Anintervening layer of insulation 10113 then surrounds the firstsub-portion 10146.

The second portion 10142 of the shield 10118 is wrapped around theintervening layer of insulation 10113 and is therefore physicallyisolated from contact with the first sub-portion 10146. The secondportion 10142 then extends on to the proximal end of the lead 10108 andis therefore axially longer than the first sub-portion 10146 and thesecond sub-portion 10144. The outer insulation layer 10120 thensurrounds the second portion 10142. As a result of this configuration,the first sub-portion 10146 is located between the termination point atthe second portion 10142 and the inner layers including the innerinsulation layer 10122 and filars 10124.

The second sub-portion 10144 of the first portion 10140 laps onto theouter insulation layer 10120 as a result of the inversion 10138. Thesecond sub-portion 10144 may then be covered by an additional outerinsulation layer 10127, made of the same or similar material as theouter insulation layer 10120, if it is desired that the secondsub-portion 10144 be physically isolated from the body tissue.

The thickness of both the intervening layer of insulation 10113 and theouter insulation layer 10120 at the inversion 10138 dictates the bendradius of the inversion 10138 where the second sub-portion 10144 lapsonto the outer insulation layer 10120. It may be desirable to have abend radius that is relatively large, such as about 0.002 inches, sothat the inversion 10136 does not act as a shield termination from whichRF might couple to the filars 10124. The lead diameter that is allowablefor a given application may dictate the relative thicknesses of each ofthe layers and thus set an upper limit for the bend radius similar tothe upper limit for the embodiment of FIGS. 79A and 80A.

The outer insulation layer 10127 may be continued to extend on towardthe distal end of the lead 10108, including filling the area where theelectrode 10130 is located. Alternatively, prior to or contemporaneouslywith the addition of the outer insulation layer 10127, an extensionlayer from the outer insulation layer 10120 may be created to extendfurther toward the distal end where electrodes such as electrode 10130are located. The extension layer may be constructed of the same orsimilar materials as that of the outer insulation layers 10127, 10120.

While many embodiments have been particularly shown and described, itwill be understood by those skilled in the art that various otherchanges in the form and details may be made therein without departingfrom the spirit and scope of the invention.

The invention claimed is:
 1. An implantable medical apparatus,comprising: an implantable lead extension comprising an elongatedinsulative body surrounding a plurality of filars and a non-conductivehousing at a distal end of the elongated body that includes an opening,a connector within the opening, and an RF pathway from the connector toa tubular shield layer within the implantable lead extension, the RFpathway comprising the tubular shield layer extended through the housingto contact the connector, the housing comprising a first layer ofnon-conductive material, with the tubular shield layer being outside ofthe first layer of non-conductive material, and a second layer ofnon-conductive material that surrounds the tubular shield layer and thefirst layer of non-conductive material, the second layer ofnon-conductive material having a thickness between 0.5 mils and 5 milssuch that a capacitive coupling may exist from the tubular shield layerthrough the second layer of non-conductive material, the implantablelead extension further comprising a plurality of stimulation connectorswithin the opening and a plurality of stimulation jumper wires thatconnect to corresponding stimulation connectors within the housing andthat extend through the first layer of the housing so as to besurrounded by the tubular shield that is outside of the first layerwhile providing stimulation pathways; and an implantable lead comprisinga shield electrode on a proximal end of the implantable lead that has anRF pathway to a shield within the implantable lead, the implantable leadbeing positioned within the opening so that the connector of theimplantable lead extension contacts the shield electrode of theimplantable lead.
 2. The implantable medical apparatus of claim 1,wherein the connector is distal of the stimulation connectors.
 3. Theimplantable medical apparatus of claim 1, wherein the conductivestimulation pathways are isolated from the RF pathway from the connectorto the tubular shield layer within the implantable lead extension; and aplurality of electrodes on the proximal end of the implantable lead andin contact with the plurality of connectors within the housing.
 4. Theimplantable medical apparatus of claim 3, wherein the isolation betweenthe RF pathway and each conductive stimulation pathway within thenon-conductive housing is at least a separation of 0.1 millimeters. 5.The implantable medical apparatus of claim 3, wherein non-conductivematerial of the non-conductive housing that provides the isolationbetween the RF pathway and each conductive stimulation pathway has adielectric constant value between 2 and
 10. 6. A method of shielding anapparatus comprising an implantable lead coupled to an implantable leadextension, the method comprising: providing a non-conductive housing ata distal end of the implantable lead extension that includes an opening,a connector within the opening, and a tubular shield layer within theimplantable lead extension that extends through the housing to theconnector, the housing further including stimulation connectors with theconnector being distal of the stimulation connectors, the housingcomprising a first layer of non-conductive material, with the tubularshield layer being outside of the first layer of non-conductivematerial, and a second layer of non-conductive material that surroundsthe tubular shield layer and the first layer of non-conductive material,the second layer of non-conductive material having a thickness between0.5 mils and 5 mils such that a capacitive coupling may exist from thetubular shield layer through the second layer of non-conductivematerial, the implantable lead extension further comprising a pluralityof stimulation connectors within the opening and a plurality ofstimulation jumper wires that connect to corresponding stimulationconnectors within the housing and that extend through the first layer ofthe housing so as to be surrounded by the tubular shield that is outsideof the first layer while providing stimulation pathways; providing ashield electrode on a proximal end of the implantable lead that iscoupled to the tubular shield layer within the housing; and insertingthe proximal end of the implantable lead into the opening to establishcontact between the connector of the implantable lead extension and theshield electrode of the implantable lead.
 7. The method of claim 6,wherein the conductive stimulation pathways are isolated from thetubular shield layer within the implantable lead extension; and themethod further comprising: providing a plurality of electrodes on theproximal end of the implantable lead and contacting the plurality ofelectrodes with the connectors within the housing upon inserting theproximal end of the implantable lead into the opening.
 8. The method ofclaim 7, wherein the isolation between the tubular shield layer and eachconductive stimulation pathway within the non-conductive housing is atleast a separation of 0.1 millimeters.
 9. The method of claim 7, whereinnon-conductive material of the non-conductive housing that provides theisolation between the tubular shield layer and each conductivestimulation pathway has a dielectric constant value between 2 and 10.